Well, sure. As you move the axel farther back, you're effectively shortening the chain a little (or effectively lengthening your chain stays, or effectively lengthening your RD hanger). The top pulley on the RD pulls further away from the cogs. Which means a lot if the biggest cog would otherwise be riding right on the pulley. Means you don't have to take out a link pair to make the small/big climbing combo work. That extra link pair, in turn, is going to make a big difference if you want to hit the big/big combo without breaking your RD.

For me, personally, having a usable big/big combo is never the question (I just don't go there). It's having the chain so it's not terribly slack on the small/small combo that it's going fall of if I hit bump. If I can do that and also not break my RD if I accidentally hit the big/big combo (hasn't happened yet), then I consider my efforts successful.