Oxidizer-only tanks & Support for transferring fuel between jet tanks & rocket tanks

[Tortoise]

Well, first I think there should be an oxidizer-only tank so you can choose how much oxidizer you want, since jet engines burn more fuel than rocket engines.

Also, I got to the moon with my SSTO and found out I can't put fuel from my MK2 fuselage to into my FL-T800 fuel tank. That sucks.

[Supernovy]

What advantage would this have over tweaking the liquid fuel out of a rocket fuel tank (leaving just oxidiser)?

A higher mass ratio would possibly offset the disadvantage of using more parts. Another option is to ignore jet fuel tanks entirely and have a rocket fuel tank with slightly less oxidiser in it than liquid fuel.

[Stargate525]

What advantage would this have over tweaking the liquid fuel out of a rocket fuel tank (leaving just oxidiser)?

A higher mass ratio would possibly offset the disadvantage of using more parts. Another option is to ignore jet fuel tanks entirely and have a rocket fuel tank with slightly less oxidiser in it than liquid fuel.

aesthetics, size, part count...