opinions on mixing with a sub?

I never mix with my sub, but I always turn it on when everything is done and make changes as necessary.

Being a car audio buff, I can tell instantly when an album was checked with a sub or monitors with good low end. Pretty much 70% of the shit I listen too sounds like hell in the low end department. And then there are albums that sound perfectly balanced down to 15hz, I can certainly tell they were mixed or checked with a sub.