Apparently Robin Williams has missed being in a sitcom, I remember Ashton Kutcher kept mentioning that when he got cast on Two and a Half Men. Still surprised he'll actually be in one again.
More stable life for an actor/actress. More like a 9 to 5 rather than a shift work type job since films can have you up at all hours like shooting a scene at 3 in the morning outside the comfort of a heated set. I've fed people "dinner" at midnight and later because of some shoots.
A good TV series is of one of the best jobs you can get in Hollywood so you can lead a "normal" life outside work regarding friends and family.