Well there're all the usual variables around conditions, terrain, distance and personal fitness, but if you want to get technical about it

:-
If we're talking general road use then we can assume a range, at the back, of anything from 11 to 28t, I know there are bigger but, due to chainlines, I would have thought most people would be in their inner ring if hitting those. So using an 11-28 as an example you get:-
53t - 127 down to 50 gear inches but 58 if you're avoiding too severe a chainline
52t - 124 to 49 or 57
50t - 120 to 47 or 55
42t - 100 to 39
39t - 93 to 37
34t - 81 to 32
The last three you'd probably avoid the two smallest cogs if they're the inner of a double/compact.
Then it's then a case of knowing the sort of gears you do most of your riding in, for me that's the 50 to 95 gear inch range. Expressed as MPH that's 14 to 28 for a 100rpm cadence and 11 to 23mph for an 80 cadence. So for a 53/52/50t ring that would be rear cogs in the range 14 to 28, whereas for a 42/39t it would be 11 to 23t cogs, and 34t wouldn't give me the high gear end.
If, for example, you ride a 52/42/30 triple, with an 11 to 23 cassette, and you ride in the big ring a lot then you're either pushing very big gears or you're using chainlines that aren't optimal, as you wouldn't be in the regular riding range until near the middle of the cassette or further.
My triple now sports a bashguard rather than a big ring and a much smaller inner, it's 24/40/bash, and I have an 11t out back for my big gear. If I get fitter/stronger then I may jump up to 26/42, 28/44 or 30/46. But it's really centered around doing the majority of riding in one ring with optimal chainlines.