I don't notice any difference at all with a load of 3000lb. It really depends on what the tow rig has for brakes. If you are towing with an unsuitable vehicle, like a Jeep or a car, God forbid, there is no minimum weight. You should have brakes, period. But, if you are towing with an F250HD or equivalent, the electric brakes won't matter for a trailer and a off road rig on it. Just a distraction, IMO. Of course, if the total towed weight is substantial the brakes are helpful. I will say though that I have seen electric brakes on a trailer overheat in the mountains when the truck brakes were not even working hard. And some guys mess around with the controller when going down a long hill to have the trailer slow things down without using the tow rig brakes (most controllers will let you apply the trailer brakes without pressing on the brake pedal) and that is just a real bad idea. Those little electric trailer brakes are not a substitute for the truck brakes. And applying them by themselves to slow the trailer, load and tow rig is just asking for trouble.
03 Rubicon; 99 xj with too much stuff to list; Unimog 406 (gone)