Let's assume that a user wishes to move away from TeX.SE and intends to delete all of the content they created up to the legally possible limit. Deleting tons of comments, unaccepted answers and unanswered questions is faster than creating them but doing it one-by-one is still a time-consuming operation; furthermore, there is a limit of 5 deletions per day on posts. Is there no faster way to do it?
The only way to perform a speedy removal of content would be via programming. Support for this is provided through the Stack Exchange API. Here you can delete a question, an answer and/or a comment, all of which require authentication (since you're only allowed to delete content if you're a/the permitted user). You are still rate-limited, but it will be much quicker than deleting the content manually.
Deleting your account is similar, but all content will remain, and all votes cast to individuals will be removed if the votes were legitimate votes and wouldn't cause too much disruption to the community. This is to avoid high-voting users (often high-rep users, but not always) from causing reputation havoc.