Hi, Zulkarnain,
Yeah, i agree to the points that A high gain efficiency can be desirable for an amplifier when a high gain is wanted.
Fiber amplifiers with small effective mode area can easily reach differential gain efficiencies of several dB/mW,
with special optimization even more than 10 dB/mW. However, it can be preferable to have a not too large gain
efficiency in cases where a high energy needs to be stored in a gain medium.
optical amplifiers are desired to operate in the saturation region in order to achieve high output power and high efficiency.
As The gain efficiency may also sometimes refer to the stored energy instead of the pump power.
Thanks