There’s a big difference between giving your horse a “treat” and using rewards during training. A treat is something given freely, without expectation or prior cause. A treat is something that the recipient enjoys, but they didn’t have to put effort into receiving, at least not intentionally. Usually it comes by surprise, and is unexpected. It’s an “every once in awhile random occurrence of something enjoyable that happens without probable cause”. A reward on the other hand is something entirely different... a reward is something earned and worked for. It’s something to be gained through effort and actions... there is cause, there is reason... its not random, but it too is enjoyable!
verb \ ˈtrēt \
a : to provide with enjoyment or gratification
c : give someone (something) as a favor ."he treated her to one of his smiles"
d : do or have something that gives one great pleasure. "treat yourself—you can diet tomorrow"
verb re·ward \ ri-ˈwȯrd \
a : thing given in recognition of one's service, effort, or achievement.
"the holiday was a reward for 40 years' service with the company"
b : show one's appreciation of (an action or quality) by making a gift. "an effective organization recognizes and rewards creativity and initiative"
For humans there are many things that can be used for treats and rewards; hugs, a pat on the back, sweet foods or candy, getting to go see a movie, money, time off from work, visiting friends, and so on. Every human will place that list in a slightly different order, from most rewarding to least, but at the end of the day most humans find all of those things enjoyable.
For horses the options are a little more limited, being simpler by nature, but we have a solid three options that we can offer for treat or reward to our horses; physical contact (scratching that sweet spot!), rest, and food! There are a few more options that we could discuss as well, but let's just stick to the primary three, with food typically being the most enjoyed of the three.
We like to hand out special foods or scratch their “sweet spots” when we are feeling extra warm and fuzzy towards our horses. We are "treating" our horses to something they enjoy for no particular reason other than because we feel like it, but there’s also a form of training that involves rewarding the horse for good behavior and actions. This is called “positive reinforcement training” and it’s involves a very different system than arbitrary treat giving. The primary difference being the awareness of timing, and the delivery of the food... I would also say that perhaps the “intention” has something to do with whether it’s a reward or treat, but horses don’t understand intention, they only understand perception.
This is actually where demonizing positive reinforcement/clicker training began. Because horses are constantly learning, you are constantly training. Even if you don’t intend to be, you are. If food is of high value to the horse (which is the reason it works so well as a reward!) and you just randomly hand out food when you feel like it, completely oblivious to the timing, you are likely to be unconsciously rewarding undesirable behaviors. Behaviors like... ears back, wide open mouths, general grumpiness, tail swishing, nose in your pocket, mouthing at your hands, pulling against the lead rope, leaning against the stall door, pawing, pacing, prancing, stamping, pushiness... all common behaviors that lead people to think their horses are rude, disrespectful, or aggressive!
For this reason I don’t “treat” my horses often, if ever really. Sometimes I will throw them an extra flake of alfalfa, or let my kids give them a treat for the fun of it, but I always pay attention to the timing. I watch my horses' behaviors and wait for moments when they are relaxed and pleasant. I watch for happy ears, still feet, closed mouths, and even nicely ask them to back up a step before "treating" them.
It's okay to feel warm and fuzzy towards our horses, and it's okay to make yourself feel good about how well you take care of your horses, but arbitrarily handing out food and good things can be dangerous. Pay attention to when and how you "treat" your horses, remember your horse is always learning and you're always training.