I asked this very question to Humber shortly after purchasing my new boat from them at the end of last year. With my previous boat, I'd deflate the tubes a bit to reduce the strain on the emergency relief valves (it was an old boat), plus I also thought that it would be less strain on the baffles.....
Anyhow, Humber suggested to me that I leave the tubes fully inflated all year around, but take a small amount of air out during the summer to prevent them being over pressured.
The main reasoning for this is that when they are inflated, if something comes into contact with the tubes, it would be more likely to 'bounce off' rather than 'dig in' and do damage. I don't leave my boat in inside storage for the year, but it will stay outside again this winter since I have every intention of using it all year round.
I'd have thought that keeping them inflated also helps keep everything in the right shape long term.
Also, I reckon now that leaving tubes inflated all at the same pressures that it would be less harmful to the baffles, which then don't have to curl up or anything inside of the tubes - I haven't a clue really about this part, but in my mind it makes a bit of sense
I know that down at the local yacht club, we leave the ribs inflated all year round, and don't bother taking air out at all. Obviously during the winter, things get cooler, so they appear deflated a bit.... when we use em, we just put a bit more air in.
I don't know what anyone else thinks?