>>64349597
Generally you don't use your sidearm so having it on your thigh and out of the way means more room on your belt for stuff you're more likely to need.
For cops, I would say having your pistol on your belt would be preferable, since you're much more likely to need instant access to it.

I don't care what you noguns say, you'll always draw faster from the hip/waist compared to a thigh holster.