I usually don't inject when just cooking for myself (but I have). Mostly because I'm lazy and always get a good finished product anyway.
If I want to impress someone (friends or judges), or I just want more flavor, or a more complex flavor in the meat.... I will inject.
"Of all the imaginary friends I've had, I don't think there was one that I didn't end up having to kill."
in seach of Umami