Not to intentionally rain on travel voucher threads, but 3 things to keep in mind:
1. Usually there is always some discount available by default on hotel room prices. When you apply vouchers like this, you will lose out on those and card discounts and pay the full (marked up) price, which may be close/more than the 20% you're saving here.
2. Different websites have different prices for the same hotel for same dates. And not all hotels are bookable on all portals. You can use an aggregator site to find the lowest one. That way you're not locked in to one portal and you may end up paying less without a voucher.
3. You may still need a valid SBI card to complete the booking. I was charged Re. 1 to "validate the voucher".
Source: I get a lot of SBI vouchers too. IMHO these are designed to be useful only to the recipient.
