i've a got a 53/39 chainring with an 11-28 10-spd cog for 20 different gear combinations on my road bike, with maybe 14 actual usefully different gear ratios, but because chicago is so remarkably and unceasingly flat, i'm almost always on my big chainring and i really only ever use 6 of the gear ratios depending solely on wind conditions.

53/28 (49.7) - bad chain alignment, i don't use it
53/24 (58.0) - bad chain alignment, i don't use it
53/21 (66.3) - strong headwind (also my starting gear)
53/19 (73.3) - fair head wind
53/17 (81.9) - light headwind/neutral
53/15 (92.9) - light tailwind/neutral
53/14 (99.5) - fair tailwind
53/13 (107.1) - strong tailwind
53/12 (116.1) - only for down hills, and living in chicago, i don't get to use it often
53/11 (126.6) - only for down hills, and living in chicago, i don't get to use it often


so for the most part, having 20 speeds is overkilll most of the time for me, but it is nice to have the 39t chainring to drop down onto when i'm traveling with the bike in places that actually have hills.