well it shows you made some kind of effort, even though a very minor plus if i were to give my 16 brother WHS vouchers he might not spend it all in the crack house but might buy something educational.
what it shows is: I couldnt be botheredd to find out the first thing about your likes and dislikes, or to think of something for myself, so instead i have decided to impose my will on you and force you to go to debenhams/wherever. This means that you are going to have to do more work than me in the present getting process.
hmmmm - altho they can be useful on wedding lists for instance if you have a certain limit to what you can spend and the bride and groom may want a contribution to an expensive item.
I think they are fine if you don't know someone very well yet, like a new "in-law", or if you're a university student and *just* started dating someone new, and are not sure that the relationship will ever even get serious. I kinda agree with FTVS and wildwood.