I agree that one would have to choose the best trail, but the image above on the left shows a trolley being used on very wet ground. I guess it depends on how much weight you are carrying.I can see it being useful on tracks or trails with low vegetation but on soft ground it will just sink in and in woodland it will get caught up on sticks and brambles and scrub.
I agree Mark, but then I'd not be towing one on the Beacons/Snowdonia/the Munros LOL