Having been paid to shoot and teach shooting for several years...
As Tritium21 points out, very much about the way we handle projectile weapons is based on two things:
- The stability and intuitive position required to aim the weapon
- The stability required to recover from firing (whether that means maneuver to acquire a second, cover oneself from harm after loosing a shot, or recovering from recoil to line up a second shot)
This is true in one way or another all the way from darts to throwing knives to javelins to atlatls to slings to bows to firearms to actual energy weapons in use today.
But a pure energy weapon has no recoil
The recovery time is whatever the recharge would entail. No idea what this winds up being in the Star Trek world, but we'll just assume its close to zero and they can shoot as much as they want... because, um... science. (That said, after personal experience with capacitor-driven microwave weapons, this could be significantly annoying.)
So that leaves us with #1, and that is mostly about lining up the shot and maintaining stability during the pull. In this case the "pull" will be a button press instead of a draw, swing or trigger-pull, but the weapons themselves appear to be incredibly lightweight -- which means either the triggers are really, really lightweight themselves (sort of scary, considering what the business end can do) or are incredibly well aligned with the natural motions of the fingers and the lines of tension exerted from whatever is defined as a "proper" grip.
This, by the way, is critical in pistol and rifle shooting. In fact, there are certain types of shooting where there is a direct parallel: slow-aimed-fire. Anything from match pistol, match rifle, Olympic-style bialthon (which uses a .22 cal weapon), benchrest and the new "lightgun" style used for the (ridiculously dumbed down modern rules of) pentathlon.
In all of these cases either a single shot is going out and it counts for everything, or the shooter is given a relatively huge amount of time to line up follow-on shots (so recoil isn't a factor aside from not hurting the shooter, as in the extreme range competitions where the guns kick a little harder than normal). The triggers on these weapons are as light as mechanics (or rules) permit, the grips are highly specialized to assist a shooter in locking the weapon to the body but with as little linear contact as possible, and the shooter assumes as stable a position as possible.
OTOH, close-range tactical shooting is rarely slow-aimed-fire. (Which is why the standard U.S. Army pistol test is not at all a reflection of combat competency but our old SFARTAETC "stress test", while still flawed, is much better -- and neither hold a candle to Bill Rogers' "reactive range" tests.)
Its all about body position
The importance of the stability of the firing position and grip cannot be understated because the trigger-pull itself is what will throw your shot. If you happen to have a laser pointer handy, turn it on, point it at a wall at least 10 feet away, and just see how steadily you can hold it on a 1-inch circle without doing anything else. Then try it sitting down. Then raise a knee sitting down and rest your hand on that. Then do it while breathing deeply. Then lay down and try it.
The magical answer to your question comes when you try the same exercise as above, but this time apply some stiff pressure from a finger into your grip. Try different fingers. Try pushing, sliding, pressing, yanking in different directions with different fingers, and watch what happens to your laser point (protip: it'll go totally wild most of the time).
To be even more accurate, put something similar to a Star Trek phaser -- like a TV remote -- in your hand and tape the laser pointer to it. See how steadily you can maintain your point of aim as you press buttons on it. This will tell you a lot about how practical the grip in the shows is.
My two cents
My suspicion is that its not a a good grip for an energy weapon unless they always lock the wrist bones down at the same angle and fully stress the ligaments on top, which sucks to do for more than a few seconds. I can't imagine that this would work out well in practice. Oh, did I mention, shoulder joints are inherently unstable...
Also, two hands always beats one; you can limit fundamental instability to just one dimension instead of three, and use opposing tension within a two-handed, cupped grip to stabilize the weapon as the trigger is pulled/button pressed/whatever. This is why gangsta-grip tends to result in a lot of sky-high fliers or ankle-level shots, even at very close range (for a right-hander they tend to be very high to the right or very low to the left -- but we're all quirky little snowflakes, which is why it is impossible to design "the perfect trigger/grip" pair).
...Unless they actually use a mental or voice activation we're not aware of. Or a button in the other hand. Or computer activation. Or... you get the idea. This would be totally badass and is the way to do high precision shots properly. But even then, its hard to hold a laser pointer at something very long with the confidence that you will destroy it (and only it) when the thing goes off when doing so with just one hand.
...Unless the energy weapon is itself somehow auto-aimed within a certain degree of accuracy. Considering we are trending toward modern weapons of this form today, I think its somewhat safe to retcon this aspect of mechanical assistance in accuracy into the Trek world.
EDIT: Something I failed to notice or mention initially, but grew curious about checking out a few Star Trek clips is that they appear to often be pointing the weapon with one hand and activating the trigger with the thumb. This is a terrible idea. The only reason we have triumphed over the other apes is our brains, but our further success over dolphins is due exclusively to our thumbs. There is only one on each hand. Without a very specialized grip that permits pressure from the metacarpal of the thumb to be the exclusive opposing retainer to all four gripping fingers (which is actually possible, but very tiring/cramp prone in practice -- srsly, try it), using a thumb to activate the trigger is almost a guarantee that you will throw your shot.
...and we'll just forget about those pesky aiming devices...
Something I did not address at all, but is absolutely critical, is the concept of "sight picture". There appear to be no sights on these things at all. Something the size of a TV remote can unhinge a bank vault door, but it apparently lacks a reliable aiming mechanism for all that power. Man, I sure hope these guys practice a lot, because they are always shooting from the hip. Shooting from the hip can be rather accurate though, out to about 25 yards. But beyond that the law of squares just eats you for lunch... (an inch off-target at 10m is how many inches off-target at 500m? You need sights on your scary-powerful energy weapon)