When poured on yourself, instead of constantly healing you, the liquid will cause you will glow. This can be useful as it negates the need for any light source.
Occasionally, Ichor merchants may sell convalessence.
You can also collect it from the 3x3 pool left by a Blue Jell when defeated.
Trying to reuse small amounts of it is likely to fail as it will turn into Cryogenic Mist.
It is required for operating the Regeneration Tanks in Bethesda Susa.
It can be used as a Cooking ingredient, granting cold and regeneration effects.