Aww, no alien empires yet

[JohnnyYesterday]

One idea for continuous expansion might be to prolong their own existence into the distant future. They might turn the rest of the galaxy and eventually even neighboring galaxies into efficient "storage units" for hydrogen. Look at our sun for example. Most of its fuel is wasted . . .

Actually, stars waste very little of their total mass-energy during their lifetimes.

Most of the mass that they started with ends up in the white dwarf or neutron star that they collapse into after the fusion-portion of their lives.

The efficient thing to do would be to leave them alone to burn themselves out, until their mass is needed in deep time.

You can "burn" any matter if you have micro black holes.
If GUT monopoles actually exist, ditto.