Decades ago, Reynolds issued an advisory against braze-on fittings allegedly due to a tube failure in the Tour. Adding shifter braze-ons to the tapering butted section of the down tube for example to an already brazed frame with "brass" is lots of heat at the wrong time. Same goes for other bits post primary brazing. Chainstays are not that much effected as the zone where most have a cable stop are are quite thick, way over 1mm. Bottom bracket cable guides typically on the top sruface of the SHELL were less of a problem. Silver "brazing" bits on is far less heat with a reasonable artisan.

In the 70's there was a slow creep to add them primarily to assist maintenance, I had shifter bosses silver brazed to two bikes to make claning them easier, yes less sparkle but much less grunge.

Now many bikes being restored are having the braze on bits removed, to restore them to original.
I will keep my modified bike as is, I did the work myself in the mid 80's when it was just an "old bike"