I am 70, so I see "getting fit" from a different perspective from many of you who are younger and fitter.
Exercise is advocated as "good for you" but I think some try to do too much of the wrong type of exercise when you are unfit and overweight.
Getting fit tends to build muscle, which makes it easier to do more exercise and burn fat.
When I joined this forum I had been disabled for about half a decade, but losing weight and getting my heart and pacemaker fixed let me start walking - and I have been walking 30 or 40 km a week, and doing a little body-weight exercise.
But did I get fit just for health and longevity... or to give me the fitness I might need to do something useful sometime?
The path I regularly walk is muddy in the winter... and was overgrown with brambles, so I took my machete with me to bush-whack the brambles and get some upper body exercise.
Then a lady called for volunteers to help spread gravel on the bit that would be muddy in the winter. I do not know if she had any idea how many man-hours it would have taken to move two tons of gravel 200 metres by wheel-barrow!
I used my trailer to get and spread gravel where I was before (the neighbour had a JCB which I used to create a camber)... so we bush-whacked enough width to get my 4WD and trailer up the path, and I spread the first tonne last Friday, and last Saturday I drove while a team of volunteers spread the second ton.
It was nice to be fit enough to help.
I have a theory that I might find the energy and enthusiasm to get some work done around my house and garden!