RB has 48 tracks vs BiaB 8-10
RB allows generating on these additional tracks (wherever you want), so more tracks to choose from.
RB has the Multiriff function, which allows generating 8 versions of the same RT (for any given section) which then allows comping these 8 (or 16 if you do it again) into one track that resembles what you want.

AUX, Subgroups and other additional routing options also separate it from BiaB.

RB is more like a DAW than BiaB, yet many features transfer over from both sides. I use it as a stepping block between BiaB and other DAWs. It feels more like a DAW but retains a lot of BiaB features.

Mainly I like RB because I can continue working in a BiaB generating fashion while still being able to add additional tracks (whether MIDI, recorded Audio, or additional generated tracks) in a more DAW like setting.
As an additional plus, once happy in RB I can just drag the tracks to other DAWs like Reaper and keep working.

Make your sound your own!
.. I do not work here, but the benefits are still awesome