As much as most would like to avoid it, it's a necessary evil in this lifestyle. Of course, not all discipline need be physical punishments and, i believe, no one should feel truly happy that discipline must be applied. Because, after all, it speaks towards a failing as both Dominant and submissive. It's a failing on the Dominant's behalf because they hadn't "trained" (for lack of a better word) their submissive properly. And it's a failing for the submissive because they didn't properly follow what their Dominant had asked of them.
A good Dominant should not seek to punish for that reason. In a way, it's like a parent; they don't want to discipline their children, but for the sake of learning and behaving, it's necessary. Likewise, a submissive should not seek to be disciplined. There's a big difference between just being a brat and mouthing off a bit, which can be playful in the right set of circumstances, and completely disregarding what a Dominant has asked of their submissive.