i do every time, but in many many years and thousands and thousands of injections i have never aspirated anything but air back into the needle.. no blood or anything. no problems.
the biggest injection related problem i have ever faced was a gusher. this was early on in my injection career and i literally used to STAB myself with the needle in the glute, not ease it in. I would just jam a 25 gauge 1.5 inch into my glute as fast as I could (i used to use 25 gauge back then, lol).
One time (and i should note i was running a test E cycle only, lol again), after I stabbed my ass with the 25 gauge, and I pushed the CC of test in and quick as possible, I then pulled it out as fast as I put it in, and blood basically squirted 3 feet onto a white wall in my old room.
Just a little squirt of blood, but it was gross.
I was a bit crazy when I first started injecting. My attitude was to have no fear, so my first injection, I literally just stabbed myself, and well.. it worked. I quickly learned by my 2nd cycle that this type of activity was for lizard people, and i also by then had switched to 22 gauge because i was injecting more. I learned easing that bitch in makes for a cleaner, smoother, less painful inject.