Hooray! Something for my sims to do between work, school, and getting laid!
Taking the time to really develop some of your hobbies into skills can provide many usefull benefits. You can create things that you can sell for one thing. And you can also use your hobbies as new social networking tools.
The introduction of secondary aspirations and life reward points adds a new dynamic to the game that will help give some of your characters much more balanced personalities. Or it will turn them into grilled cheese sandwhich addicts.
But most importantly, there are a bunch of new items and ways for you and your sims to express their creativity.
And overall, the more you put into Free Time, the more you will get out of it!