Originally Posted by FBinNY

It's so rare that we disagree, that I can't pass it up.

While B/B+1 is bulletproof with modern slant parallelogram derailleurs, who's idler cages can rotate enough to clear a straight line along the bottom of the sprockets, it can fail miserably with an older non-slant derailleur. Those lower pulleys cannot swing above a nearly straight lower loop and the RD will be torn off. (wasn't rare BITD)

Older RDs on vintage bikes must have the chain measured big/big, through the RD cage (a la Homebrew) and pulled up short of tight (one inch or so).

And AGAIN, any big/big method is about the minimum length, but you have the option to go longer.