I don't know, but I would assume it's similar to setting CPUTYPE in your make.conf so binaries are built with some cpu-specific asm for your specific flavor of

I don't know, but I would assume it's similar to setting CPUTYPE in your make.conf so binaries are built with some cpu-specific asm for your specific flavor of x86 CPU: you'll get a performance boost, but nothing mind-blowing.