The primary purpose of a ring or vacuum clamp is NOT to remove warps but to more tightly couple the record to the mat or platter surface. When a stylus runs in the groove, it is actually elastically deforming the groove and the groove then rebounds. This creates a lot of vibrational energy imparted to the record. The tight clamping of the record to the large surface of a mat or platter dampens this energy and also drains that energy off for dissipation in the much larger mass of the platter. This accounts for some people finding the sound to be a bit dead or overdampened (a matter of taste and system matching).
I have a table with a vacuum clamp (Basis Debut). In use, this is far easier than a ring clamp, and, I don't have to worry about accidentally hitting the cartridge with the clamp or the needle getting snagged at the clamp/record interface. If I did not have a built in clamping device, I would use the ring. I like the less hashy sound of the play with clamping than the slightly more lively sound of play without the clamping.
I have a table with a vacuum clamp (Basis Debut). In use, this is far easier than a ring clamp, and, I don't have to worry about accidentally hitting the cartridge with the clamp or the needle getting snagged at the clamp/record interface. If I did not have a built in clamping device, I would use the ring. I like the less hashy sound of the play with clamping than the slightly more lively sound of play without the clamping.