That it's an "Old Fart's tale" is just another Young Whipper Snapper's Know-it-all fallacy. It depends on how much reflected power the particular TX's RF output stage can handle at the ambient temperature. Best to play it safe.
Case in point, from Futaba's FAQ: (Old Farts need not read on)
"When I am using my radio for programming, setup within my house, experimenting, etc, is there anything special I should do? You should ALWAYS extend your antenna at least the bottom or first segment when turning the radio on with a module in place. If left in the radio with the radio on at your work area with the antenna collapsed for more than short intervals, the module will be unnecessarily exposed and may shorten the life or even immediately damage the module/transmitter."
Ye Olde Fahart