Well actually there is, because the clock starts ticking from the time of the PCR test, and not the RAT test. If you are involved with travel, or need to take leave from work etc, then the PCR is the "official" test for many.
I see a place for RAT tests, but they are limited in my view unless they are incorporated into the overall reporting system. As
@Flashback mentioned, the UK ones have a QR code to upload the results. I have heard no similar plans here around that, although perhaps National Cabinet is in deep discussions as we speak. For now I view RATs as self protection rather than community protection.