You have some great help here from the replies. I will will give you my take.
First up, in the normal run of things you would like to have a full range of frequency response. But (1) the midrange is where most of the music is; (2) The avoidance of crossovers is a benefit - but this is (a) mitigated by quality (whatever that is) designs of the crossover and (2) systems (eg ATC) where all three drivers in a three way system have similar cone designs. (3) And this is my main point: it depends on your music. Say your real interest is in string quartets: then the benefits of a single driver come to the fore. Disclosure: I have not heard a single driver system.