That might depend on where the piano was made [& how carefully], its intended market locale & whether it has subsequently been moved from that location.
A good piano maker will season the wood it is to be made from in the country of the intended final destination so the entire seasoning is done in similar climatic conditions to those in which the finished instrument will eventually live.
Once seasoned, the wood is vac-wrapped & shipped to the factory, where the entire production line is then set to match those climatic conditions.
The piano is built in those conditions, vac-wrapped again & shipped back to where the wood was seasoned, for sale.
Under those circumstances, the only conditions I would even dream of messing with the humidity would be if the piano was being kept in a hot, dry environment - like a centrally-heated house - in a predominantly cold, damp climate; thereby unbalancing the makers initial consideration.