Certainly in the UK, the SDI Solo Diver is the only one accepted for diving in one of our lakes (Wraysbury) -- all others are solo hostile. They will not accept the PADI self-reliant diver certification.... and where would you rank the SDI Solo and PADI Self Reliant certs ?
Have never been asked for a certification for solo diving off a boat -- have dived off of many and am nearly always solo even if diving with someone (who will also be diving solo).
To the point: the Solo + Self Reliant certifications are a very challenging and a significant achievement for a recreational diver. This is much less so for technical divers who are, or damn well should be, well versed in redundancy, shutdowns and switching gas, plus planning, core skills, monitoring, etc.
The certifications are a demonstration that the diver has the right solo attitude and can handle multiple failures with redundant kit.
Most people should aim to do those workshop/courses if only to be more self reliant. Buddies are all well and good, but they will not always be around when you need them especially in poorer conditions; visibility, currents, in and around wrecks.