Originally Posted by santiago

You don't need to change the crankset to get a different number of teeth, you can simply change the chainrings.

Changing the cranks is usually done because:
- you are looking for something stronger
- you are looking for something less flexy
- you are looking for something lighter.

With respect to flexy, we're talking about the crank arms. Imagine pedaling down on the cranks and feeling the crank arms giving and bouncing. That's flex.