One thing that confuses me and hasn't been made 100% clear is how often UK nationals need to use the machines / kiosks before queuing for passport control.
I assume you only need to visit the kiosk machines to register on your fist visit. And then once every 3 years? But I know travel journalist Simon Calder has shared multiple videos of him registering, implying that it needs to be done each time (and for some reason he seems to make it seem so confusing and such as hassle, even though it only takes seconds in reality).

Certainly, I have visited Europe twice since the launch of the EES. Firstly, at Prague I used the kiosk to register. Secondly, at Riga I just walked past the kiosks and went to the border officer who processed me.

But, other than marking my diary, how will I know when I need to re-register? What happens if I reach a border officer when I need to use the kiosk? Will they turn me away, or just re-register there? It all seems very over complicated and makes me realise how much the UK spoils much of the world with its e-Gates.

Once stamping is withdrawn by the EU, will they resume use of the e-Gates for UK passports?

It would be good to get some actual answers to this! If registering for the EES is required each time, then they should add some kiosks to key UK airport departure areas such as LHR / LGW / MAN.