There are many reasons why you might want a tv script. If you are a fan of a particular show then as well as a script being a great piece of memorabilia to have it also gives you a deeper insight into the characters as it often contains direction and extra information pertaining to them. It may say for example 'Sam looks away, and then fighting back the tears he responds with'... or 'They exchange a knowing look and suddenly realise the horrible truth, almost as one they say'...This extra kind of information can be fascinating to read and is something you're not always aware of in a visual representation of the script.
Scripts are also useful reference points for budding writers. They can show them how a script is put together and gives them an insight into what would be expected of any script they intend writing.
Of course a script of someone's favourite tv show makes an excellent and slightly quirky gift - especially when they already have all the DVDs and related merchandise.