I happened to be down in Bristol earlier in season and made last minute decision to go to Bristol City v QPR. I was informed no tickets could be bought at the ground, but I could buy a print at home ticket. Was staying in a hotel and it was going to be a hassle so I queried it with the ticket office. They said that I could just scan the code from my phone and 99% of time it worked. They just couldn't advertise them as anything but 'print at home because 1% of time it didn't work. Anyway I had absolutely no issues. Most likely same situation for other clubs with 'print at home' scanners