These soldiers who had been to the battlefield were hot commodities for nobles with a certain amount of power. After all, they didn't require much training; if the master needed, they could directly be sent to the battlefield to serve their new master, especially during wars, they would be excellent cannon fodder.
Even if it wasn't wartime, they could also be used for some heavy labor. Physically strong soldiers were much better to use than skinny, bony serfs, and their strength was also greater than ordinary slaves.
