The big advantage BIAB has over arrangers is, it KNOWS what the next chord is going to be (you already told it!). This allows it to walk basslines from somewhere TO somewhere at times, something no arranger can, because it never knows what the NEXT chord is until you play it, by when it's too late!

The thing about writing is, by its very nature, its SUPPOSED to be 'original'. The more generic a backing you put around it, the less 'original' the song sounds. On the whole, when working with arrangers for songwriting and demo purposes, I tend to use the arranger 'capture' as only a jumping off point. I'll erase everything I can play better than it (at least I know the next chord!), and edit as much variety into the Parts I can't play better than it (usually the drums and guitar parts).

But it's great to have a fully fleshed starting point. That 'build it up one Part at a time' way you usually do with workstations isn't nearly as quick, and often the results take longer because you have no guide track to help you with 'feel' and groove.

Anyhoo... back on topic. On the whole, I can get away with just a couple of styles if I rarely play that genre. But stuff I do a LOT, I like to have as many as possible. But with one caveat. They got to ALL be of pretty much the same quality, or you tend to only use the best one or two. I'd rather do that than have some naff style just for variety, though.

Problem is, most arrangers are chock a block full of oldies styles I wouldn't use in a million years, and painfully short on much that is contemporary and pop, especially non-electronic pop. I would happily trade every last cha-cha and cumbia for a few more 'Live band' styles, alternative rock/pop, and you can never have enough funk and New Orleans grooves!

All in all, if I were an oldies fan, I'd be in heaven... but I'm in 'hip' style hell!