I recently rejected a suggested edit to Count the subsequences of length 4 divisible by 9. The edit suggested to add codechef. I didn't know what Codechef was, but it appears to be an online programming competition where you can win money and "goodies". I rejected the edit, I thought it would be better as a comment (at most).
From the answers to Is there a policy on questions taken from prize-bearing coding competitions?, the consensus appears to be that it's OK to ask those kind of questions, as long as they fit SO's format.
However, in my opinion we don't need to organize the information according to programming competition. I'd say code competition tags are useless clutter at best and deliberate advertising at worst.
I found these competition tags on SO, there might be others (feel free to add them):