If you’ve ever trimmed a horses hoof you can say with certainty that yes at certain dry points of the year hoof dressing is a must!! I grew up watching my mother do farrier work and now I do my own. Unless you want to stick all four hooves in water buckets and wait an hour you need hoof dressing. If it’s wet and rainy don’t bother with anything except maybe some iodine on the sole to help with any hoof rot that will develop if your horse has to stand in mud. During dry seasons I mix pine tar and vegetable oil in equal portions. If you get a mason jar and a paint brush you can rig up your own applicator too. It’s the best! It stays on good and makes nice flexible hooves so your farrier will love you and is it’s so much cheaper than the other products out there (some of them hardly work at all).
Hoof dressing is needed because we confine our horses and limit their access to different kinds of footing. Wild horses get their hooves wet when drinking or walking through a stream. Our horses don’t normally have that access. You can try to create that by overflowing your water bucket though if you don’t want to put on hoof dressing.