I've been looking at the stable (or gun safe) and been thinking about this. I've got a lot of great rifles, but they're all very different.
I'm trying to make High Master in NRA Highpower and I practice at the range several days a week. If I had two identical rifles then I could easily swap between them to run through a 50 or 80 round practice match as fast as possible. It would save a lot of time by not waiting on the rifle to cool between stages (in an attempt to preserve barrel life). I was doing the switch barrel thing for a while....I'd practice with one, then spin on the match barrel for matches....but eventually life happens and it's midnight before a match the next morning and you realize you didn't swap barrels and confirm zero after your last practice session. Then you think about driving 2hrs to shoot a match with bulk reloaded ammo with an SD of 50 (exaggerating, but you get the point).
I just put a new barrel on my match rifle in 6XC.
Honestly I would love to have the same rifle in .308 to work on recoil management. I can work on mechanics by dry firing....no second rifle needed.
Even now, I often take other rifles to the range with me, but they have different stocks/triggers/actions/scopes. I hesitate to shoot them because my positions are different, the sight picture is different, and the trigger is different. Regretfully, I may need to sell a few things to standardize a little bit.