Think of potions class as your regular Chemistry class. It's not there to make you a master potion maker (no one comes out of high school as a chemist), but to give you some understanding of what potions are, how they are made and what effects they might have.
For instance, a wizard who goes through his potions lessons might, later, recognize the effects of a sleeping drought. Or recognize a love potion before taking it . As in our chemistry classes, they will learn that two ingredients interact with each other in such a way to, for instance, stop the effects of the first one. This could be very useful if they later needed to quickly stop the effects of a simple poison. Just how we learn that acids will react with bases creating a salt and water, for instance.
And besides that, there are the reasons that have already been mentioned in other answers.
The potion classes (again, much like our chemistry classes) will teach the students how to use some equipment that wouldn't be used in other settings, such as cauldrons. It is also supposed to teach the students the main, simple potions which they will probably need at some point in time.
And about the books being misleading, and potions being a "Follow the Recipe" class, well potions will also take a lot of cooking if you think about it. But with maybe disastrous results when something goes wrong. Which is why it's important to follow the recipes: to make sure nothing goes wrong. However, the better you get at it, and the more intimate you are with the subject, the more room you'd give yourself to experiment. Which is really what make the real masters.
So, in someway, that would also be the aim of the potions class: to make the students intimate enough with potions so that they would be able to later experiment and not HAVE to follow the recipes all the time.
: We see that during the Half Blood Prince, when Slughorn asks the students to recognize different types of potions. That would be useful if they were in a situation, for example, like the one on the first book, where they had to choose from a few potions the one that was safe to drink. No potions class = being clueless, and depending solely on what information is given. With the potions class they'd be able to make some assumptions and rule out some options.