Yeah. But on Star Trek only the three stars had to be used every week. Regulars mostly meant recurring, specifically Rand, Scotty, Sulu, Uhura and Chekov, and, at best, they had a guarantee of X out of Y shows ("contract"), but the reality was most of them were mostly on an as-needed-and-available basis, so no contractual guarantees at all, characters like Scotty were cut from scripts if it was cheaper to use a guest actor for a day than pay Doohan his guaranteed rate.Plus, the regulars are under contract and have to appear every week (though that's seemingly less the case now than it used to be), so you have to contrive excuses to use them even when another character would make more sense.

