Erdin:
For a power supply the transistors are not in saturation.
I also have a power supply with three parallel 2N3055.
The transistors didn't match very well, but I compensated that with a slightly different base resistor.If a transistor is used in saturation (as a on/off switch) a very minimal difference will have a large effect.
In linear circuits you add a small amount of emitter resistance (if necessary) to promote fair-sharing of
current, and mount them on the same heatsink close together (so Vbe will be matched).
In theory you could use the same trick with switches, at the expense of more heat loss in the emitter
resistors - but it would need tuning to the actual load current.
The key point about BJT's is that Vbe drops for a given current as temperature increases, so the hotter
device turns on more, gets hotter, the colder device is starved of current and cools down - thus the
important of mounting on the same heatsink.