How often to clean out deep liter?

I put my chickens in their coop back in May (6 months ago). I started with 2-3 inches of wood chips and added a 1/2 bag every couple of weeks. I must have an average of 5-6 inches in the coop now....more where they "hang out", less under the nipple waterer and feeder area (they seem to keep that area almost to the floor). From what I have read, it seems most people clean out their deep litter every 6 months...spring and fall. Is this necessary, or is this schedule to accommodate their composting schedule? To be honest, my liter doesn't look too bad and is dry. I was thinking of just adding 2-3 more inches to it for the winter so they have plenty of liter to keep them warm on the floor and wait until Spring to clean the whole thing out. Opinions?