Much of it is aesthetic for me, and when function and numpad keys are rarely used, that aesthetic doesn't really get in the way of utility.
Also, for those with small desks, it's very nice to have the extra space. A tenkeyless or 60% board is also very easy to transport (I drag mine between two different workplaces and home every week), and the fact that I can reach any key on a normal keyboard while barely moving from the home row makes things a little more efficient, albeit a little less comfortable.