In moderation, with common sense, of course its good for you.
In extremes though - yeah if I were to try to run for the bus I would probably die, but then I have multiple health issues that make that a stupid thing to do in my case.
If you push your body to the limit, theres a higher chance you will hit that limit, a school friends mum died in her early 40s, she was INCREDIBLY fit, ate a very lean diet, ran, swam, skied, climbed, worked out ... and had a heart attack on a golf course which she didn't survive. In her case, her bodies limits were lower than she'd realised, on the other hand had she not been as fit as she was, perhaps she'd have died far younger?
I am now 4 years past the 10 years the specialist cardic lot at Manchester gave me... I do pretty much fuck all, my exercise is rolling over in bed and going upstairs twice a day to the loo and to bed. Exercise won't help me now and I did plenty of it when I could, it may be why im still here... or maybe its why bits of my heart are dead. I don't know.
Some people really do push it too far, gymnasts and ballet dancers spring to mind, they start before they're finished growing, and they are often badly damaged by their 20s or 30s.
Be sensible eh.