There is a straightforward no quibble full cash refund if a mistake is noticed within 24 hours of booking, but requires a telephone call, whereas the eVoucher alternative can be done online. But they can also fix mistakes too, such as name spellings. In the old days this was a way to avoid change fees, though you would still be on the hook for any fare difference. If you are travelling before October then there are no change fees, so that doesn't matter now and the ticking clock isn't so important for date changes, but the fare difference remains an issue, the longer you leave it, the more likely it is to change, usually upwards. This does not apply to online BAH bookings, where there are different rules.

I know some people on this forum get their spouses (etc) to do a double check before committing big sums to airlines. If you spend too long booking the dates all start to blur.