If you are running a hydraulically powered implement and you get stuck, turning off the powered implement would be the first thing I'd do just for the safety aspect.
By turning off the implement, you won't gain any hydraulic flow to the wheel motors, as the PTO pump is separate from the tram pump. However, you will get some more engine power available for the tram pump to use.
HOWEVER.... the main PTO pump is always pumping, wether you have it turned OFF or ON, it is ALWAYS PUMPING! The main PTO switch on the dash is not an ON/OFF switch for the pump; it's an ON/OFF switch for an electric diverted valve. When OFF, it diverts the output of the main PTO pump directly back to the tank. When ON, it diverts the output of the main PTO pump directly to one of the main PTO quick connects out on the FEL arms, through the implement, and then back to the tank through the other main PTO quick connect on the FEL arms.
So, if you're stuck, and leave the PTO pump ON with an implement running, the implement will consume some engine power that could be used by the tram pump if it were turned off. Even if the implement is just free spinning in space, its consuming engine power because of air drag and inefficiencies in the hydraulic motor on the implement, drag on the fluid in the fittings and hoses, etc...
Does that make sense?