To some people, inflicting pain for punishment is considered the "easy" way out. I think that the kind of punishment used depends on the people involved and what would work best for that particular mistake. One option is to have the submissive write about the error, why it was wrong, what possibly caused it and what they can do to avoid repeating it. Another is the removal of privileges, such as ordering that the submissive can not masturbate without permission., removing computer time, or similar things. In some situations and for many submissives, just knowing that they have displeased the dominant is punishment enough. Many submissives are mentally harder on themselves when they have erred than the dominant ever could be.
This can be utilized as a very effective way of constantly reminding the submissive to never repeat such a mistake. By denying closure, one leaves the guilt as a reminder. Some people use withdrawal as a way to punish. This one is tricky because it can spark emotional problems of abandonment in the submissive. This should be discussed before hand as a possibility before being used. For some people, if the infraction was severe enough, they might remove the submissive's collar until such time as the submissive earns it back. As you can see, the ways to punish vary greatly and with a bit of forethought a very effective means of non physical punishment can be thought of.
