Possible Scenario:
Self Biased SE amp, with a 3K primary OPT.
Short the secondary output common and 8 Ohm Tap.
Now the primary impedance = ~ DCR of the primary.
The output tube is only 1 DCR away from B+
Now, suppose you do not remember that the speaker is not connected, and you do not hear anything, so you turn the volume control up, but not enough to draw grid current. Or you turn it up even more, draw grid current, possibly blow up the cathode bypass cap and bias resistor.
The poor output tube is drawing more plate current than it was ever designed for (for roughly half of the time).
. . . No, I will not try that trick to see if anything gives.