Yes and no...
I have to keep the girls fed, so offers like these are good for buying cat food in bulk. Tesco prices on a box of 12 or a box of 40 are pretty competitive already when compared to Wilko or Zooplus, so when you add the money off, plus the clubcard points, it's a worthwhile exercise. Though people DO give you strange looks when you've got fifty or sixty quids worth of cat food in your trolley.
Otherwise I'll just use the voucher for an ordinary shop and top it up with things like toilet roll and bubble bath and canned / dry goods that I use anyway. Though I'm luckier than most when it comes to storage space, and so CAN do things this way.
I don't go bananas with these kinds of vouchers though, and if I don't actually need anything, they don't get used.