I delete when I feel a page is OffTopic. BeBold; after all, anyone can remove the mark for deletion in the next two weeks if that's what the community decides. Marking something DeletedPage is in a way more of a suggestion than an action, so I do it freely when I feel that the rest of the community will agree.
I would suggest you not do this until you've been hanging around for awhile, though, so that you first get a feel for what the rest of us consider off-topic.
-- BayleShanks