More precisely, disabling the autonomous addressing flag in the router advertisement packet allows you to completely control the addresses which will then only

More precisely, disabling the autonomous addressing flag in the router advertisement packet allows you to completely control the addresses which will then only be handled by DHCPv6, which allows you to slice a /64. But that means no v6 temporary addresses for anonymisation, which might be exactly what you want in a managed network/corporate scenario which requires liability tracing.