At the simplest, Lend Energy (Healing college) and paut (as defined in Dungeon Fantasy/DFRPG and from GURPS: Thaumatology) are both intended to replace Fatigue Points spent in casting magic (faster than resting would).
However, the Thaumatology description of paut also states that if you drink more than required, the excess remains, and can be used for casting up to an hour after the dose. I never knew that until last night, because I've never owned or handled a copy of Thaumatology.
This, including the realization that GURPS has thousands of pages of rules I've never seen, leads me to ask whether the same is true of Lend Energy -- that is, if Alice the Mage casts a small spell, and her apprentice Bob the Younger uses Lend Energy to restore her fatigue, but miscalculates and Lends a couple more points than needed, will Alice be able to use that excess energy to cast without further depleting herself? Or will it be wasted? Or is there some other outcome?