Breaking this out from the current stable update thread (18 June 17).
Phil replies to the effect that 'Yes, it's essential'. However, I'm through the update, things are working fine, and it's not installed ... so I'm holding off for now.
Somebody smarter than me can tell me if that's a bad plan.
My guess is that like elogind, it's sort of the way things are going, and will eventually be mandatory, but it's not yet.