My truck uses oil, sometimes quite a bit of it, so I usually check that every time I drive. I stopped putting TCW3 in the gas (ran out, forget to buy more) so it's back up to about 1 quart every 200 when towing (yes, there is a cloud of blue smoke trailing me). My Jeep I check every time I use it, usually once a month.
The Subaru has a low oil level light so I don't check it as often. With the exception it used 1/2 quart over 6K miles on M1 AFE 0w30, it's never used any oil. So I don't worry too bad.