i think its all to do with how we've been brought up to think.
back when it first started (i have no idea when that is) i would suspect one person did it, and like everything that is once done, people see it and copy it if they liked it, so more people started to do it, and soon it became normal to do it. well thats my theory
why anyone would ever think of removing hair in the first place is like asking, why some one would ever think of cutting their hair in the first place... people experiment, for different reasons looks or maybe it was benificial (ie, stoped lice etc...)
and i supose it grew on people and became to be what it is now
i agree with TOTT and making you look more youthfull
and i also think it has become part of fashion (looking good) people think certain hair styles look good, just because they do, or because they've been brought up to think it looks good (i have no idea if im making any sence now)
so my conclusion is for why people do it at the present, is because its been around for as long as we rember, and we think it looks better.
people do it because they think it looks better. just because its what they think.