I’ve seen lots of people get obsessed over their “fit” looks, and sometimes them going to the gym is both caused and made worse by more obsession with fitness.
Personally, it helped my confidence a lot and made me happier in my body to hit the gym. Seeing progress in something where you have to have grit and dedication usually does help people boost their confidence though, like learning an instrument or a new language, especially in children. Nothing as rewarding as meeting one’s own goals, if you ask me.