Increaseing the number of blades will reduce the load on the prop. This is done to allow a smaller diameter of prop and therefore a lower RPM for the same performance. A lower RPM means less noise as the tips have a lower velicity and are more efficient (less turbulence from sonic tips and a nice ride from the cockpit).
This will also increase the take off performance as SOLIDITY (aspect ratio of the blade disc) is increased. The other way to do this is to increase the blade chord, but this will effect the gravitational forces on the prop and as it produces more lift, the CTM force will twist the prop to fine with massive stress, obviously reducing efficiency.
If solidity is increased, so is drag at idle power......it will drop like a brick on the threshold so land with a squirt of power and once over the TH, reduce it at the same rate as you want to sink when in ground effect.
SOLIDITY=number of blades x chord/2PYEr (if it helps)
JD