To use them as often as possible will save on maintenance.
This might (qualified) be correct, however, IMO, safety overrides savings on maintenance.
One must remember that 90-series KingAir aircraft are certificated under 14CFR23
which absolutely does not guarantee the performance margin that a 14CFR25 aircraft would, in the event of an engine failure on takeoff...IE: you
need all the performance margin you can get with these airplanes, in the event of the unfortunate happening.
I have had an engine failure in two BE99 aircraft just after takeoff (200 agl, approximately) and even with autofeather fitted, the climb rate was
very marginal, as we were heavy.
I say...safety
first, possible maintenance costs savings, second.