There is no need to be registered, and the Care Act has removed the advantage in so being which previously existed. Although s77(3) Care Act replicates the requirement for local authorities to maintain a register, the repeal of the Disabled Persons (SCR) Act 1986 has removed the automatic assessment requirement and statutory entitlement to services (since these were deemed to be unnecessary with the introduction of national eligibility criteria).
Whilst registration used to be seen as stigmatising, nevertheless it may still be one of the very best things a care manager can recommend someone with a disability to apply for. Whilst it no longer leads to additional legal entitlements, it may still tend to have the effect of pushing the person towards the front of the queue for scarce resources.