The new Virgin Trains East Coast booking engine (currently in beta) will bring back the ability to purchase mobile tickets (m-tickets), a feature removed from the old site after a number of problems with the old 'Ticket Wallet' app but now m-tickets have had their time and should be replaced by e-tickets which are much more flexible.
What's an m-ticket and 'Print at home' ticket
An m-ticket is a mobile ticket which has to be stored in a special app. You can't store the ticket in your phones built in wallet app (such as Apple Wallet) and you can't store your ticket as a screenshot of the barcode in the photos app. The app as a number of security features such as an animation showing the current time. This is so ticket inspectors that weren't equipped with barcode scanners could still do some validation on the tickets. Most ticket types need activating before you travel.
The main drawback with m-tickets is the ticket is tied to a particular device, although most apps will allow you to release a ticket and send it to another device it is not possible to print out these tickets if you lose your phone or your battery is running low. You're also at the mercy of the app that stores your ticket, if it starts crashing when you're on board the train this can be an issue.
It's not possible to change an m-ticket to a 'print at home' ticket. A 'print at home' ticket MUST be printed out. They have the right to refuse to accept print at home tickets if you show them on the phone, although some guards will accept them. The reason why print at home tickets need to be printed is they have a special pattern on the background that makes it easier for the guard to spot a forgery should they not have a barcode scanner.
What's an e-ticket?
An e-ticket is a much more versatile ticket. A few rail operators including Virgin Trains West Coast, CrossCountry, Grand Central and Greater Anglia now support these. This means that those responsible for checking tickets on their route are all equipped with barcode scanners and they no longer need the limitations imposed by m-tickets. With an e-ticket it's the barcode that's important. You have a choice of adding the ticket to you phones wallet app, displaying it in your ticket purchase app, showing the barcode in your confirmation email on you phone or printing it out. It gives you flexibility and means you're not dependent on a buggy app to display your tickets.
Unlike print at home tickets, there's no need to print them out but you have that option. The only reason to print out the tickets would be if you're concerned your phones battery will run out or if your phone has been lost, stolen or damaged.
It seems crazy that VTEC are rolling out a site that supports the old m-ticket format and the inflexible 'print at home' tickets while the West Coast have been offering e-tickets for almost a year now and other operators have now followed suit. As all VTEC staff are equipped with the barcode readers and they're launching a new site it would make sense if they supported the option that works best for their customers.
A word of warning
Some booking sites will offer e-tickets for operators that support them, but will offer m-tickets and 'print at home' for other operators that have not (yet) rolled out e-tickets. So when booking tickets online please check the rules for the ticket you've purchased and if in doubt the safest option is just to opt to collect physical tickets at the station.
These days most train guards and revenue inspectors have the appropriate equipment to scan the barcodes on e-tickets so these should be rolled out across the network and the less flexible m-tickets and 'print at home' should be retired.