Since you just said FI and not ER, it's definitely been not worrying about the little things. I feel like I have better control over my life and make better decisions because I can think more about the big picture and ignore *every little purchase*. The Finance Buff once said that the opportunity cost of his ER is similar to spending a significant amount to not work. On the flip side, I am FI but still like my work, so if I go to a new restaurant that sucks or feel ripped off for the quality, I don't stew over it like I did on the way to FI. Little luxuries like tipping well, using toll roads to save time, buying popcorn and soda at a movie theater, fast passes at amusement parks - I never would've thought I'd be a frivolous spender like this. I guess it is surprising that I got to FI, then got to 2x my FI number, and then the wealth building snowball just kept going... and yet, I still can't justify buying an overpriced luxury car nor do I want a more expensive house. Did put my daughter in private school and my wife can be a SAHP (she substitute teaches sometimes for fun), these are luxuries that I am grateful I can afford.
Now that I'm an expat, I'm glad I didn't ER yet, but I'm always on the lookout for a good time to start shedding the 35hr job (I'm in France). Work has a lot of nice perks and I enjoy the project and team I am currently with (and learning about my French colleagues is fun, as a tourist, you don't get quite the same openness and willingness to discuss at length in English). But it's nice to know I don't have to work if things aren't so rosy in the future, which will probably happen when I return to the US. Mais tu ne sais jamais!