Hardly ever. I clean my droppings boards every morning, which helps enormously (also helps with air quality/humidity). Every several months I do some spot-cleaning, mainly of dust from spilled food near the feeder, and add a bit more clean bedding. That's pretty much it. I think I did about a 50% change of my sussex pen about 18 months ago, but don't recall for sure. '
It helps that I have relatively few chickens per pen, so that poo in the bedding has time to sort of disappear rather than getting all matted together with other poo into a nasty glump.
JME,
Pat