I always release the tension on mine (a little, really not very good Einhell bench top machine, I forget the size). I do that because I bought Steve Maskery's (Workshop Essentials) set of band saw DVDs and he says in the excellent explanations you should do that.
BTW, IMO those DVDs were one of the best few quid I've ever spent for workshop stuff (despite the loads of stuff on the internet about setting band saws up - usual disclaimers, he's "just" a member of this Forum). AND I wish I'd bought those DVDs BEFORE I bought the band saw - I might have made a better buying choice, especially as before I bought the machine I doubt that I'd ever even "walked past one" before!
Even if you think you know what you're doing, unless you've been properly taught how to use and set one up, personally I'd highly recommend you buy those DVDs.
I don't think it's possible to over-tension any blade on a cheapo machine that has a casing made of welded up pressed steel sections like mine - I guess it would all start to buckle before the blade broke! Different story with a "proper" machine with a STRONG, cast/& bolted casing though I guess.
BTW, because the DVDs said to always de-tension the blade after use (and I don't use the machine all that often) that's what I do. I have a cardboard sign on a piece of string hanging on the tensioning knob which say "Tension Blade - About 2 Turns". As soon as I tension the blade before using the machine I turn the sign face away, and as soon as finished (for the session) I slacken the blade right off (to approx. the same point) then turn the sign face out again.
A silly but serious-ish P.S.- When typing the word "blade", 99 times out of 100 I type "balde" instead. Dunno why. Anyone else have that problem (AFAIK I'm not dxselctic) ;-)