Engine Braking

[Vitaver]

Consider that the engine/exhaust brake (or switching to a lower gear on manual) do not activate the actual brakes on either, the TV or the trailer. The problem is obviously with the trailer brakes not slowing down the trailer on a down slope can/will either push the TV or sway, perhaps dramatically. If you use engine brake, you may want to manually operate the trailer brakes first and during.

[Andrew T]

If your hitch is setup properly the amount of deceleration created by engine deceleration is not going to cause any loss of control unless your on snow.
If you’re on a long hill you would overheat the trailer brakes long before reaching the bottom. Use the trailer brakes when slowing for a switchback or to decelerate to get into a lower gear.