Provides labour opportunities for farriers, saddlers, leather-workers (reins, stirrups etc.) and riders. Useful for knights to ride (it enables them to out-run the peasants easier). The catch is that, since the horse can carry their weight, the knights tend to wear heavier armour, and then they (the horses) being vulnerable to good missile fire, they (the knights) tend to find out why heavy clunky armour doesn't go well with fighting on rough terrain, against lightly-armoured, and therefore more manoeuvrable, opponents.
Comes in two flavours: stallion and filly. There is also an 'off cut' of stallion called gelding. Don't ask (if you have to) you won't want to go there!
In terms of the medieval life, there were war horses, "ambling" horses (which, in England, became known as "hackneys" (after the village and marshes east of London wherew a breeding line was established), "working" horses (i.e. agricultural proto-tractors), and carrying horses, the medieval equivalent of the commercial van.
Not normally eligible to become a landed or court noble, or archbishop. Possibly a good candidate for royalty, where there is a capable First Minister already in place.