206 hydraulic shutoff check
K48, I was told that the hydraulic check you refer to checks that the hydraulic cutoff switch works normally. This is also common to other helos.
Quick review of the fundamentals- the hydraulic cutoff switch energizes a valve that blocks flow to the servos, thus reverting to non-assisted control, and, hopefully eliminating boost issues by eliminating assist. If the switch is defective, it won't shutoff flow and whatever hydraulic assist issue you had could continue until you land.