In terms of damage, 5 minute chess can spoil your appetite for the harder work of longer time-controls, but I don't think it actually damages anything. Mostly it's a (fun) waste of time -- you don't learn chess playing 5 minute IMO -- some people disagree with me, but I don't think you even get better at blitz, by playing blitz, (you get better at clock management... but you don't actually learn to make better moves.) You might memorize a few openings that way, but that's about it. I think blitz is where you show off how good the vision and instincts you've developed via slow OTB chess and study really are. Generally, strong long time control players play strong blitz chess. ( CC players are a different animal IMO... although CC is good training IMO.) By the way... those 10 and 15 minute time controls you play are blitz -- 30 minutes is considered "rapid" -- a good real chess game is supposed to take a couple of hours.
My bottom line: play blitz for fun... if you want to improve, play long time controls against strong players, and study study study.
As all those who have read my profile already know, I've only learned the game a little over 9 months ago. And in those nine months I've seen a decent increase in my ratings playing almost exclusively 10 to 15 minutes per side. But a few weeks ago I stumbled across a group of gentlemen in the park that meet up every weekday at a certain time at the local park and they only play 5 minute games. Just by observing the games and the strength of each player I can already tell they are stronger than I am so when they ask if I'd like to play I respectfully decline and let them know that I'm not ready for 5 minutes per side especially 5 minute games against players of their calibur.
In order to try to get to that level I've been playing 5 minute games on chess.com recently with horrible results. Although I've gotten myself in winning positions in most of my games I've managed to squander my advantages with ridiculous blunders and giving pieces away along with the game. Is it because i'm still too green and need more overall chess experience before I step up to become a formidable 5 minute player or is it because I've simply not played enough 5 minute games? I'm a little conflicted by this and wondering if anybody has a few tips.
And another thing, I really wanna take one of these guys out but I also don't know how much damage if any I'm doing to my overall game by playing 5 minute chess and such an early stage of my chess playing.