Thanks to alistairlees for the clarification. So, to get a print-at-home ticket, I would first need to realise that I making one of the very restricted journey types for which print-at-home tickets are available, work out which TOC I would be using for that journey, and then set up an account with that TOC. I can see why the print-at-home ticket option is not well advertised! OK I suppose if you live in an area that is only served by one TOC, and rarely stray out of that TOC's area.
But what if you are not offered that option? The TfW web-site, for example, encourages you to buy your ticket before boarding. It also specifically states that the requirement to have obtained your ticket before boarding only applies if your point of origin has ticket-buying facilities. So, as far as I can see, if your point of origin does not have ticket-buying facilities, you are perfectly entitled to buy your ticket on line, and to join the train without having obtained (i.e. collected) the ticket.
I have just bought a ticket on-line, and as FortheLoveof says, you are only able to select collection stations that have TVMs, but it did allow me to select a collection station that is not my origin, and I was only asked to confirm that I realised that it is not my origin station. At no stage was i told that I must collect the ticket before boarding the train. The email confirmation that I have just received states that I must collect my tickets, but again it does NOT say that I have to collect them before boarding the train. Again, the requirement to have obtained your ticket before boarding does not apply at stations that don't have ticket-buying facilities. So, as I see it, I would be doing nothing wrong if travelling from say Barmouth to Euston, in buying my ticket on-line, and selecting say Birmingham NS as my collection point. As long as I collect my tickets at some point during the journey, surely I would have met all the conditions? What would I be doing wrong?
This would be no different than if I were travelling from say Belper to London, selected Belper as my collection point, but when I turned up at Belper station I found the TVM wasn't working. I would be perfectly entitled to get on the train without a ticket (as at that point in time the station had no operational ticket-buying facility), and collect my ticket at Derby.