I've just flown in recently and was asked for the printout. Your hysteria over this is bizarre. Pathetic name calling over someone saying they printed a piece of paper. You're just a weird guy looking for an excuse to be abusive.
I was asked for a printed ticket so yes, printing was useful. Lost phone/broken phone/ no signal. . So instead of you wasting time whinging about "killing trees" try some commonsense.
It's all online and they already have it. But it's an extra level of confirmation in case they require it. I never rely on technology and printed mine.
I put where I boarded and started my journey, UK. The connecting flight was delayed and flight number changed so it would have been pointless to put that, especially as I didn't start my journey there. It was accepted as UK and I'll stick to that next time too.
Why are you trying to fill it in outside of the 72 maximum? It clearly says not before 72 hours. It's a few minutes task with very little to fill in on it. You can even do it in the airport, the plane or on arrival.