I knit really tight. It bends my skinnier needles, and sometimes it's difficult to slide stitches from one needle to the next.
Basically, as long as you can move the stitches without bending the needles or putting a blister on any of your fingers, you're fine. You just have to be able to adjust your needle size so that you can match someone else's gauge.
I find that I typically hold my needles just a bit too tight, but holding the needles looser does not necessarily change my gauge.
How tight or loose you knit is a personal thing, and there is no such thing as the perfect amount of tension. There is a "good" range... and if you fall outside of that range, well, as long as you can make adjustments... who cares?
If you knit tight, I recommend metal or plastic needles. The wood ones feel nice, but they grip your yarn more and make it harder to slide. Also, metal/plastic needles often have sharper points (in my experience)