I know its a cliche but for me - healthy body=healthy mind. As someone who is prone to depression and has a stressful job as well as family with 3 teenage girls
I know the value of exercise goes well beyond the physical.
The egotist in me also likes being in better shape and fitter than 98% of people my age and most people half my age.
... And of course I am vain and anyone who says they are not is kidding themselves.