Yes and no. The pros are obvious, of course; being healthier, stronger, the confidence boost and more attention really are great. Athletic activity opens up a completely new world of entertainment. But there's also a somewhat dark side to it, or at least there is for me. A nice body can be alienating to some people. One big problem I encountered is that my body change resulted in some horrible jealousy issues with friends, both men and women. My social groups from my youth were the typical party/bar crawl crowd, and we did it up majorly. However, as we hit our late 20s, the lifestyle caught up with us and we started getting fat. Of course we all made the pact to work-out together and eat healthier blah blah, but I was the only one who followed through with it. In my friends' defense, our lifestyles were grossly unhealthy, basically just working to get to the weekend to do drinking and smoking with little sleep, up all hours, no exercise besides walking from bar to bar. So going from that to consistent working out (working out with smokers lungs is one of the most horrid experiences) and moderating caloric intake was akin to throwing a fish on land and demanding it to walk. But it does suck because when I hang out with my friends, it's me and bunch of drunk, overweight, depressed smokers making snide comments about how I spend too much time in the gym or my "obsession with my body is weird." They basically hold a grudge against me for it which has really changed our dynamic. I've had three girlfriends who've said they don't want to be seen with me publicly because they think I make them look fat by comparison, past FWBs don't want to sleep with me anymore because they don't feel attractive enough, etc.. Contrary to what others have mentioned above, I haven't really enjoyed more sex with hotter people. I definitely sleep with hotter guys now, and that's nice. However, in my midwestern city, fit isn't really the norm; for every 50 guys I interact with on grindr or in a bar or wherever, there's maybe 3 or 4 who I'd consider, (and whether I meet their standards is another matter as, admittedly, I don't have a typical attractive male face), and the logistics and practicality of hooking up sometimes completely leave me with nothing (I'm not traveling 40 miles round trip for ass or waiting an hour for them to come over). I've also noticed that a lot of guys assume that, because I'm fit, I will only date or hookup with other guys at my same fitness level, which is not necessarily the case. But, like the issue with my friends above, the disparity in physique is alienating so they don't approach me or try to engage. Far too often on Grindr I hit up guys who say they've wanted to talk to me but feared some bitchy, insolent rejection. Also, a profile pic with a muscled body attracts a lot of catfish, so most of the time half the hot dudes hitting me up are fakes or bots or whatever.
But, with all the above said, I don't regret it in the least. Working out and lifting feels great, it's great to be healthy and get healthier, it's wonderful to care about what I eat and to be able to breathe properly again. I now enjoy getting sweaty and dirty and being outside in nature (I was something of a fuss pot in my youth), I care less about superficial commercialism (no body cares what you wear or what label you wear when the body is what's being eyed). It's really tempered me in a lot of ways and turned me into a much more mature adult than I was in my 20s. And one thing to remember is that getting slimmer or more fit doesn't necessitate hours in the gym or starving oneself. Sometimes all it takes is a few moderate shifts in diet and some more fast walks around the park or doing some jogging around the block. Building muscle is hard to do without a gym setting. But my first year, despite not having a gym membership, I actually made great progress in toning my muscles, and even gaining muscle, by just doing simple body weight exercises like lunges, pushups, crunches, etc.. Maintaining a healthy and strong body is very worth it.