I assume this deal works out quite favourably for Virgin.
Say you hold a return portion of a SOR from, say, Manchester to London, I believe it costs £296 at the moment.
The best thing to do would be to get a refund for half of it (£148 - £10 = £138) and then buy an Off-Peak Single (even better Return for a few pence more) ie roughly £74. The First Class upgrade fee on top of that is £15. So you're roughly £50 in pocket and hold a return portion that can be used within a month.
Instead, some people will get on the train and use a very valuable ticket on a mediocre service!