<Parapharsing the OP here so no one confuses it with the above posts:> It is a good idea to use extra protection on the horse’s legs while trail riding, even if the horse has no need otherwise for any structural deficiencies that would necessitate leg boots?
I would suggest that if the terrain warrants it - ie: nasty rocks, pricker scrub, bushes, unmarked trail, tangled vines, etc - that it probably won’t hurt to add leg protection designed for the trail (please note the emphasis). Personally, I would not use anything lined in fleece or neoprene due to the greater possibility of trail debris accumulation under the boot. I have found less damage to hair and skin using the old fashioned leather lined boots.
It the terrain is more “civilized” - nice dirt or sand paths - I personally wouldn’t worry about leg protection.
If it makes you feel better to boot the legs regardless of the trail conditions, then go ahead and do so. After all, it is your personal peace of mind that you want in order to have a relaxing, fun ride without the worry of your horse being accidentally hurt by that trail. 