normal females are of limited use. for figuring out new genes you want to keep things simple.
but for new and nice combos, both the male and the female need to contribute something. with a normal female, you cannot hit something more awesome than what the male brings to the table. if you breed a spinner or pewter to a normal you can get more spinners or pewters, sure. but make it an enchi or pastel female or something like that, and you might hit a triple gene combo you have never produced before.
there are lots of single-gene morphs on the market and prices are really coming down for some of them, which on the one hand means you shoud try for clutches with more nice combos in them to get more demand for your hatchlings, on the other hand it means you can get nice single-gene females rather cheaply and easily.
But then, when you just happen to have a normal female, and you are getting into breeding and getting the equipment you need anyway, and you just want to keep her for whatever reason (attachment, 1st pet snake, something you particularly like about her), i also see no reason to not go for the extra clutch. even if you wont hit new stuff this way, an extra clutch is an extra clutch.