The wider Brooks saddles (B66, B67, B72, B73, B135, B18, B190) are intended for upright riding, and are Brooks' "City & Heavy Duty" line
The medium-width Brooks saddles (C17, B17, Flyer, Conquest) are intended for semi-upright riding and are in Brooks' "Touring & Trekking" line
The narrow Brooks saddles (B17 narrow, B15, Swift, Colt, Team Pro, C15, C13) are intended for aggressive and/or drop bar riding, and are in Brooks' "Road & MTB" line.

Personally, I use a B17 on two of my drop-bar bikes, a Team Pro on another drop-bar bike, and a Flyer on my drop-bar touring bike and on my Jones-bar fat bike. I don't feel like the B17 is too wide for use with drop bars, but I do have my bars relatively high (tops level with saddle) and I'm a large guy (6'1" #225 ).