For me, it was both for 'priming the pump' (damn, I love that phrase Ozme ) and punishment, although it was generally more severe as punishment. And boy did I hate it. Not only could I hardly focus on anything BUT orgasm after a few days, it affected me emotionally quite a bit too. The symptoms were remarkably close to PMS, in fact.

After a while, we decided that it was more severe than I was prepared to handle for now. So we only do the 'tease but not allowed to cum yet' part, not the restriction for days.