Much like the wind that gives you a small boost of speed when you pass through it, I thought it'd be nice if there were occasional tufts of grass that you could walk through on a horse to restore something like 3-5% pony power. Something that is mostly worth going a little bit out of your way for hitting, but not able to be used to keep a wild horse around forever. Would also help make longer journeys slightly better in that it would promote active play (as in watching the map while you walk to look for the buff) instead of passive play (walk in an efficient straight line towards your objective).
While not quite a "buff" in the sense that it doesn't actually give you a status effect for it's duration. I needed some way to differentiate from it being an item that you pick up.