Since most of my travel is MR / weekend vacation, I don't like to use my miles as that would mean I don't get EQMs. However, I am not made out of money, so I will use miles when I have to be some exact place on some exact date and flights are pricey.
I try to keep around 100K-125K in my account, partially because I really like the idea of having enough for a trip in business to most anywhere in the world.