On an oil based or synthetic system, retention of oil on cuttings is the number that decides whether the cuttings can be disposed of and what it costs. A vertical dryer is the machine that gets you there.
The dryer spins cuttings against a fine screen at high G, driving the fluid out through the screen and discharging the solids dry. Recovered base oil goes back to the active system, which is the second half of the economics: you are cutting disposal cost and buying less base oil at the same time.