What does the term efficiency mean when talking about quantum memories?

Lots of papers about quantum memories talk about the efficiency generally or the storage/retrieval efficiency as a figure of merit. What exactly does this term mean?

My intuition would be that it would be related to the fidelity between the state that goes into the memory and the state that comes out, since I would have thought that was the most important figure of merit, but the same papers also talk about fidelity, so it can’t be that. And why is it important that it is high?

My understanding of quantum memory is that you want to store a state for a long time with little decoherence, but that seems to only depend on the fidelity.