Results - first off, I am not looking to lose weight (although I'll never complain if I lose 5 pounds
) however....I AM looking to maintain fitness, strength, muscle tone, all that stuff, and seeing as I am coming up on my 58th birthday soon, all this stuff becomes more and more important.
So with that being said, I mainly use cardio/strength circuits (which I happen to LOVE) to mix up things. I think I maintain cardio endurance and strength better when I do straight cardio sessions and straight strength sessions.
But if you do the same thing all the time your body adapts...so I do throw in circuits. Plus they are just plain fun for me.