Normally, I play with aging on, because I want my Sims to progress through each life stage and its accomplishments. However, I've had to turn aging off in my current game because a) I want my older Sim to reach the top of the gardening career, and promotions take forever once you get to level eight; and b) I want her to get all her plants to the 'perfect' stage, which is no longer possible within a normal Sim lifetime.
I'd get rather bored playing with aging off all the time - eventually, my Sims have maxed out all of their skills and there's just not much left for them to do.
