I think the aim, and it is a perfectly reasonable one, is to stop people getting really ill and in dosing as many people as possible they will help relieve pressure on hospitals.
My concern is that this has no data during trials, and so we may find countries (just UK at present) advocating a longer schedule have a lower efficacy than other countries. This could potentially mean us having to revaccinate much earlier than necessary. Potentially of course, it is also potentially possible that this turns out to work fine.