Every 6 months I do a proper clean. But I regularly give it a quick wipe out and I keep a tray on the bottom to catch over spill that I just pull out to wash.
When we first moved in here, the oven had so much build up, it was gross! If it was from our own doing, I wouldn't mind so much, but it felt yuck to be cooking in someone else's mess. I spent 2 days soaking & scrubbing (several times) to get it clean, so I'm too stubborn to let that go to waste. Cleaning the oven would have to be one of my most hated chores.