Philosophers of "political art" have to think about pleasures and pain because they create a framework to evaluate goodness and badness (i.e. laws).
It's also important to deal with them because pleasure is said to lead to happiness. And we're still talking about how to get happy, right?
Here's the question of the year: is pleasure good? Aristotle says that it's generally not thought to be so.
Problems: 1) pleasure is a process, but goods are complete in themselves; 2) moderate people don't dig pleasure; 3) pleasures distract from prudent thought; 4) everything good is an art (pleasure is not an art); 5) even children and animals love pleasure (eew).
Pleasures can also be shameful, which isn't good.
Some also claim that pleasure isn't an end in itself, which makes it less choiceworthy than other things.