I have found that the use of the B-string depends on what type of music you're playing. For instance, I play a lot of Rush songs, which certainly don't use the B-string. Unless of course you count the Dropped-D song Driven, in which I can just play standard tuning using the low D on my B-string, but otherwise Rush songs do not necessarily use those lower notes. However, if you're playing something like Dream Theater, where the low notes are frequent, it's much more useful.
Not only that, but when I've been tested on double-octave scales in music class, the low B string is really a beneficial thing, as I don't even have to go far across the neck to play the major and minor scales in both octaves. It really allows for much smoother flowing playing. I think it all depends on what you're playing and what notes you need to access at what speed.
Personally, I've found that the low notes have a very powerful feel to them, especially when playing heavier styles of music. I've experimented with playing an octave above those low notes in Dream Theater songs, like Root of All Evil or Dark Eternal Night, while playing with the recordings, and it feels so much more powerful with the lower notes.