I considering making the most of a character's strengths roleplaying. After all, is that not what people do in real life? The military sends people to training courses for things for which they have some natural inclination. Someone who can barely hit enough targets to qualify isn't going to be going to sniper school. People with a gift for numbers become accountants and business people. People with artistic inclinations become graphic designers. People who have a knack for journalism become full-time retail workers.
It's the same in D&D. Someone with a 9 Dexterity isn't going to become a thief. Oh, he might try, but he'll end up losing a hand (or dead) before he learns any real skills. Someone without a certain strength of will is not going to be able to treat with outsiders for power as a warlock, and so on.
And that's really where I start to draw the line leading into min-maxing territory. If you're taking classes with no real expectation of roleplaying that class (i.e. my friend, who took a level of cleric because he read it would help maximize his utility as an illusionist wizard), then you're min-maxing. If you're playing to the strengths of the character itself, them, you're "optimizing."
I guess you can figure out that I don't look fondly on multiclassing as a general rule, and it's true. To me, multiclassing is a way to show a change in direction of a character's adventuring career. A class is not just a collection of mechanics, but also an expectation of theme. You should have seen the incredulous look on my friend's face when I reminded the DM that his posh, rich character would have to wake up with the sun in order to pray. "Why would I need to do that?" Dm: "Because you're a cleric." Good times. Good times.