I often see interesting but off-topic questions. Should they still be downvoted, or is flagging as off-topic and leaving a comment enough?
Depends on what version of off topic they are. If the question is well researched but simply doesn't fit the exchange it was posted on, then the close vote/flag may be enough.
However, if the question has not been researched, is a commonly asked poor question, or is clearly disregarding of easy to recognize standards then I think a downvote is appropriate as it helps to discourage other users from repeating the same type of post.