If you're playing a cash game, you sure can. Feel free to jump in and out whenever you like. Tournaments are a different story, once you're in, you're in. Of course, you can decide to take a break or even abandon play, but you'll automatically fold/whittle away your chips as blinds/antes until your stack has disappeared entirely. So if you want more flexibility, it's kind of a no brainer in the cash game vs tournament debate.