The surface area of the wing is directly proportional to the amount of lift produced (google "lift equation" if you don't know this one already). Increasing the number of blades is one way to increase the surface area.
With every design change comes a compromise. More blades means a more complex head, potentially more components, storage can be more difficult (than a 2 blade), etc.
Another way of increasing the area are to increase the length of each blade, but that means you have a larger rotor diameter so you need bigger landing areas, more strength requirements for the blade, and you will experience compressibility effects at a lower forward airspeed.
You could also increase the blade chord to increase the surface area, I think the biggest issue here is you get more blade twisting concerns, and center of lift changes (becomes a structural issue). I'm sure other ppruners have better detail on the pros and cons of increasing blade chord.
Matthew.