We use a portion of ours to pay for RAC cover, so every year it saves me spending £250! 
We have used Tesco vouchers for this for about 5 years.
We have a Tesco credit card which we use for everything we possibly can to get the vouchers. We pay the credit card off every month though. We don't actually shop in Tesco but still get points wherever we shop.
We have just had a kitchen extension built and used the credit card to pay for the kitchen, appliances, flooring, the garden was made over so we paid for the sandstone patio with the card. We haven't got a huge limit we just buy on it and pay loads off to free up more credit ie the money is in our savings account to pay for stuff but we use the card to its full benefit.
We use it for magazine subscriptions, RAC, days out (legoland would have cost us over £100 if we hadn't used vouchers,) jewellery, restaurants, and recently it paid for all our bathroom tiling because Topps Tiles was on the deals!
Oh and buying things from Tesco direct when they "double up" so eg I was looking at a kitchen aid but they are £300 if I paid for it in cold hard cash, but I only need £150 of Tesco vouchers to get it now or I can use as many vouchers towards it as I like. So If I only had £50 in vouchers, it gets doubled to £100 so the kitchen aid would cost me £200.
I never use it against a food shop because online I can get that £10 voucher to be either £30 or £40