If you're fit, and people can tell that you have muscles even with clothes on, you're going to get way more social points than if you were a fat lump of dough. This is true in ALL personal interactions, including business. A guy with a lean waist and pecs that stand out is going to get further than a pathetic neckbeard with a gut that sticks out. It shows that you're willing to put in the work and you have discipline. This is the "opening of the doors".
If nothing else, being fit and staying that way is going to make your life into older age much less painful, assuming that you aren't pushing yourself physically to the point of damage or taking a bunch of roids that are going to shrink your balls and turn you into an emotional basket case.
However, if you're so shallow that you can't see any value in life other than fvcking hot b!tches then I really don't know what else to tell you. Once you've built your body, you just keep it up so that it stays that way, just like you don't stop cleaning your house once you've cleaned it once. If you neglect it, it'll go to sh!t.