Vouchers are either cash or points there were a lot of changes during COVID that made the vouchers a lot more usable.

I just used a BoA (US) CC voucher to book a one-way from the UK to the US. As a US based individual I don't see much value in the vouchers ex-US due to the insane surcharges. Ex-other countries they can be a good deal. What that means is I have ever only used them one-way. Today when I booked a one-way award the VS CSR (as an aside the VS CSRs are some of the best, I don't recall ever getting a bad one) said I would only be using half my voucher and that the other half would still be available for a one-way booking. That hasn't happened before and he mentioned it was new. Interesting development if true.

The math for my booking worked out to 17,500 points (premium economy) upgraded to Upper Class but of course on the hook for upper class surcharges ($725). Still the flight would have been $1,893.50 cash (half of a round trip) so I'll call that a good use of a voucher.