Mains transformer VA rating and musical power.

many many years ago, i asked a guru here about the size of the traffo for amps, and he answered me, "get the biggest one that can fit in your box."

being a traffo designer/builder myself, i would say, the number one factor is heat, how much heat are you willing to tolerate?
i guess, commercial amplifier manufactures consider the costs more than anything else...
then you ask yourself, how many hours of use per day?
are you doing full power testing? or simply just playing music, these to have an impact....
so to me there are considerations.....which one is yours?