Being outside for a kitty is conducive to increased physical activity, natural stimulation as well as acts as an outlet for their natural instinctive cat behavior.  There are risks however.  They can be hit by a car, for example.  I have always had my kitties enjoy the great outdoors.  I had adopted a 7 year old declawed cat.  She was so fat when I first got her, her stomach rubbed on the ground.  She was obviously uncomfortably fat !  It wasn't until I let that poor thing out that she started to trim down.  Not having claws didn't slow her down.  She could take on any challenger and box them to defeat.  She was the best mouser I have ever had.  She lived to the golden age of 18.  That cat's whole disposition changed when she was allowed outside.  She went from ornery to fun and active.  Just sayin...