Humm… that’s a good question… I’ve been shooting mainly landscape of late and I find myself barely using the 17-85mm…
I think that the 17-85mm just gives you a little bit of everything… 17mm being wide-ish, 50mm is usual used for potraits I think and then 85 lets you get in that little bit tighter…
That’s just my 2 cents… I’m sure other people will have different views.