THere are two problems with it on the axle of a trail rig. first it will get a lot more abuse. it is unsprung so much more vibrations jolts ect. In addition any time you go through any water mud ect. the winch will be submerged, so if you are like me it will always be covered in mud, dirt, water, run through the sand, and any other trail issue that you could immagine. The combination of these factors will probably significantly shorten its life span.
the second problem is that once you are stuck you have to figure out a way to get to it. That's an issue when the mud is up to the hood and you get to go diving to see what you can find. then not only do you have to get the cable, but you also have to unlock and lock in the motor. you may be able to remote the cable to a fairlead on the bumper, but that may break suspension parts when using the force required to pull the vehicle which will also be compressing the suspension. ANd what if the cable gets bound up under 3 feet of mud. then you will really have a mess on your hands.
A final thought is that you may have a difficult time keeping the power and remote cables from wearing out or being broken or cut. for rock crawling it would be less likely than snaging on trees ect on the trail. just like an arb line, and we know how vulnerable those are on the trials. the problem with these is that if you do have one snag and it shorts you are liekly to have a fire which could be dangerous.