In the movie 'Independence Day', they decided to launch a nuclear strike against the alien craft hovering over L.A. and the scene cuts to five B2 bombers flying at about 10k feet in tight formation like fighter planes. When the order is given to 'launch', a single nuke is fired at the craft. The burning question is; What were the other four bombers doing and where did they go? That plane is for solo high altitude bombing missions, not pack hunting.
The bombers took off in formation. they then split off to there individual targets. the bomber who launched its nuke on the L.A. ship was the first to reach its target. when the recon unit on the ground reported that the ship was intact the president recalled the other planes. he knew that they would have no effect on there targets.
During the first dropping of the atomic bomb over Japan, there was a fleet of 7 aircraft who assisted in some way, including two in the detonation zone. The other one carried a sensor package. They both executed the required maneuver to avoid the blast of the bomb. The other aircraft carried weather, photographic equipment, and other sensors. I would assume that all aircraft executed the required maneuver to avoid getting blasted, although only the two had to execute a very sharp maneuver.
As to why they did it in the movie, it could have been as happened in World War 2, or simply as a backup in case one (Or more) of the planes was destroyed. It is also remotely possible that the other planes did drop bombs that weren't seen, or they were saved in case of a different strike order being given. Some could have been decoys as well. There are a number of possibilities.
Based on what we see in the script, we can assume that they simply returned to base :
On the monitors as well, we can see the target remain. The air is let out of the room, everyone deflated.
PRESIDENT : Call them back.
NIMZIKI : The other bombers might have more luck. We shouldn't just give up...
PRESIDENT : I said call them back.
As the technicians call the bombers away, the President sinks into a depression. His last hope of survival gone.
In the official novelisation, the tone is rather darker. President Whitmore is clearly contemplating using the remaining nuclear weapons to make the world uninhabitable for the aliens, even at the cost of making the world uninhabitable for the remaining human population:
“Call the other planes back,” Whitmore said softly.
Nimziki couldn’t believe it. “The other bombers might have better luck,” he argued. “One of their destroyers is enroute to Chicago. We still have time to intercept it and deliver multiple warheads. We can’t just give up!”
“I said call them back.”
The president sank into a chair and stared up at the ceiling.
The failure to inflict any damage on the aliens’ ship convinced him there was no way to prevent them from landing. Suddenly, he felt like there was plenty of time. Somehow, he knew from his mind-meld experience with the captured alien, it would take them a couple of years to move the entire population down to Earth from the mother ship.
In light of what happened in Houston, it seemed to be time now to rethink the strategy of fighting the aliens and time to begin organizing ways to resist them once they began their invasion. The only logical course of action Whitmore could see was to wait for them to establish their cities, then blow the world to smithereens. Mankind was going to be exterminated, he knew, without mercy. If we’re lucky, he told himself, we might be able to take them down with us.
In universe, they probably wanted to see if one weapon would be enough and go on to the next target if it were. Silly militarily, but under pressure people are known to make silly desicions.
Out of universe, it just looks nice on film. If one B-2 is canonical of US airpower, 5 are even more so (and larger groups are easier to spot on the big screen as well).
While solo weapons by design, it's not unheard of for such to be used in groups. Take the B-52 which was in its current form designed as a solo penetration bomber to strike deep in the USSR with nuclear weapons, is now used almost exclusively in groups for conventional bombing missions.
As to the aircraft being more visible in groups than alone on radar, it doesn't really matter. One B-2 looks like a small bird at any distance where detection could mean interception before it can launch its weapons, in a group they'd look like a flock of small birds, not something radar operators are trained to be alarmed about (and I'd not be surprised if many radar installations are set up to filter out such small size targets to avoid cluttering the displays, and/or operators trained to ignore them).
If I remember the film correctly, there was a dispute about the other bombers. After seeing that the first bomb didn't work, the president had the others turn back. I distinctly remember something along the lines "Maybe the others will have more success". The dispute ends with the president firing his military counselor, or whatever position that was.