Do you mean the slotted, "fish turners?"
If so, three main purposes.
They're very thin, which can be very helpful especially if you don't know to cook things so they release or how to use a spatula.
The slots prevent air pockets, so food doesn't stick and slides off. That's hardly ever a problem for me, usually the opposite. That is, lose your focus for even a second and stuff wanders off the spatula.
Enough cynicism. They actually are gentle, and extra good for delicate, crisp (but not Crips') fish skin and fragile crusts and breadings. Probably a necessity these days in a professional, high-end kitchen -- especially for those who cook fish. Worth fooling around with, but the quality brands get dear. Dexter makes very good ones at a semi-reasonable price. Some are cut with a (usually right) "handed" bias, you want to watch for that if you're buying.