I can tune the same guitar many times.
i play in standard, drop D, Drop C#, Drop C, D standard, Drop B, Drop A#, and C standard.
I need six: three guitars and three basses. I play in Drop C, Drop B and Drop D.
I play in standard, half step, drop D, drop C#, drop C, C standard, and drop A# and want at least two guitars for each tuning.
It's easier to go between tunings on stage if you have a specific guitar for that tuning.