There are four aspects to this:

1. Weight: I've been 50+ lb heavier than I am now and I, personally, hated it. It makes everything harder and that only gets worse with age;

2. Fitness: this one is (IMHO) less extreme than weight differences but if you can't walk up a flight of stairs without getting winded that's going to impact your life in negative and real ways;

3. Health: when you're young this is less of an issue but as you get older being overweight and/or unhealthy becomes a more significant risk factor for many health problems. Heart disease, strokes and a host of others;

4. Quality of life: getting fresh air, sunlight and exercise is generally good for your state of mine. At least, it's good for mine. It can help put thing sin perspective (professional and personal) and improve your mood.

YMMV

As far as time goes, this was a big motivator for IF for me. As in, the effort of preparing (or even buying) meals annoyed me. It's one of the big things I appreciated about working in tech: the free meals. Not for the quality necessarily but primarily for the convenience. I don't have to plan for (many) meals.

Treating eating as a leisure activity can be a trap too like some people have weight issues because they like food and end up treating it as a reward, which reinforces the cycle.

I prefer to think of food as necessary fuel.

But how much time do you spend on food?

I'm not sure about GP, but about a decade ago I decided to stop being fat and lazy and started playing soccer, running, and later doing BJJ and some strength training (cannot seem to stick to weightlifting, but bodyweight works well for me). After that change, I slept less, but better, and had more energy throughout the day and into the night. I got more time back by being in shape than I lost from the exercise to get me there. And I was spending time with friends when I was exercising anyways (friends from before I started exercising) by joining their soccer team, going for runs and hikes and rafting trips with them, and similar things.

At work I became more productive because I wasn't struggling through half the day feeling fatigued and worn out, or pushing into a panic attack from all the caffeine needed to keep me conscious. Outside of work, despite (and as mentioned in many cases because of) the exercise I spent more time with friends and family. And I probably bought more than 2 years at the end of my life. I was on track for a heart attack in my 40s the way I was going.

I think that the bigger impact is improved quality of life when you’re old. Having a higher baseline health after 70 allows you to enjoy your later years much better. You may not live much longer but it’ll more likely be a longer period of relatively good health with a steep decline at the end as opposed to a long gradual decline where you’re able to do much less for a long period

> also means you're spending x times more of your productive years exercising

I'd strongly recommend finding some sort of physical activity that you enjoy, rather than seeing as a chore.

If you're fit exercise is a pleasurable activity, and the side effects of feeling better and looking better are pretty awesome too.

Quality of life is usually better for those who exercise and that becomes particularly evident as people age. But either way it's literally just like a totally false tradeoff - the time I spend with people hasn't been at all compromised by exercising and you can even exercise with other people too (e.g. friends at the gym, beach, going for a run with partner etc.)

I think if you've made the choice to just not exercise you should be honest about why instead of inventing non-problems like exercise significantly reducing time spent with family and friends. I literally don't know anyone who has ever raised this as a problem. Maybe if you're exercising as an Olympic athlete...?

Exercise is a long term investment though. Life really is easier when you're fit. And all the gains you get in your younger years cannot be easily done when you're older especially for muscle mass.

This specific amount of cardio fitness is probably not strictly needed. Given the choice I believe most people should chose more strength training. But at any given time, being able to pop out at least a 5km run or equivalent is probably a good place to be.