I have macroalgae, 3" sandbed, a bit of live rock, and have seeded it twice with pods.
Originally, the refugium was meant to be just that: a refuge for things you want to keep but cannot survive in the DT. Things like seahorses, that are too slow to eat and cannot compete with regular fish for food. They are now used for other purposes: nitrate export and pod propagation being the most common.
The ideal refugium would drain by gravity to the DT to allow the most number of copepods to survive the transfer to the DT. I find that impractical for me, so I have it drain to the sump, then pumped into the DT. I may lose some copepods, but that's the breaks.