Originally Posted by
Sy Reene
How people use the range of their cassettes, IMO is personally-driven decisions -- based on fitness, cadence and what the current terrain looks like. There's no universal 'should be'.
The point is that whatever position cog in the cassette, where you personally feel you should be moving to the big ring, changes when you change the starting point of the cassette. If you think it should be the 4th cog (14-tooth with an 11-xx cassette), then with a 13-xx cassette, then it becomes the 16-tooth). A wider ranged cassette offers a wider range for EACH of the crankrings. Same goes on the low-end: eg. a XX-28 vs XX-34. You pick up some addt'l low gears available using the xx-34 while remaining in the large chainring, potentially avoiding more frequent need to downshift to the small chainring (depending on your terrain, etc)..
Let's say a person has a 50/34 crankset and an 11-28 cassette. Even though they *could* use the 34/13 combination, there is no advantage over the 50/19. The 50/19 runs smoother, wears the chain at a slower rate, and still has plenty of runway in both directions. So personal fitness and terrain don't enter into it.
It's not like I'm going to make "citizen's arrests" when I see people tooling around in their small-small, but there are no mechanical or physical reasons to do so, only personal quirks.