Since the Schellas Hyndman era of FC Dallas, the club has had a core philosophy centered on Homegrowns and young'ish foreign talent, usually South Americans. The idea is to buy/sign young talent and develop them rather than going after higher priced, prime of their career veterans.
While the foreign signings FC Dallas has landed aren't usually as young as the Homegrowns the idea is the same; grow the players to contribute to the first team to either help the club compete in MLS or perhaps to be sold on. This isn't exactly a unique model worldwide, but it's not common in MLS.