The fluted chamber prevents the case from "sticking" to the chamber walls when fired, it "floats" on a layer of gas between the case and the chamber.

A "roller locked" action isn't really locked at all, the action is actually a blowback and depends on the case backing out of the chamber when fired, imparting rearward force to the bolt system. However, on say a .308 G3 the weight of a bolt needed to work properly as a blowback would weigh well over 30 pounds. To make the bolt system a reasonable weight, the rollers add a "mechanical disadvantage" to the process, sorta like using a lever reversed, where the force is applied close to the fulcrum and the load is way out there on the long end of the lever. This delays the opening of the bolt to after the pressures have dropped to safe levels.

Some calibers like the 9mm have been made without flutes (clones) and function OK, but AFAIK, all rifle pressure rounds need the flutes.