Actually defending means just a public presentation of your work. Nothing more.
Are we still talking about defending a Master's thesis in Poland?..
I graduated from UMK (Torun), and I must tell you, my defending was a full-fledged exam, including direct questions about my thesis, questions about bibliography I used, and general knowledge of the topic in a much wider spectrum than I actually wrote about. Definitely not a simple formality.
Does the paper have to demonstrate any practical value?
It depends on your field of study. The 'practical' ones will need you to present your practical skills, while the more theoretical subjects will not. However, in Polish universities, there isn't that much stress put on it. As I gather from most of the previous posts it is widely regarded as a flaw, but personally, I don't think it's that bad of a viewpoint.
My university professors used to say 'if you want practical skills, go to vocational schools'. It was a huge overstatement, but still there is some sense to it - Master's degree is neither a practical skill course nor a PhD. It doesn't make you a scientist, it mostly proves you have the grasp of the the topic, you can compile data, understand it, draw conclusions, present them and back them up in a form of a long text. It's great if your conclusions are somewhat practical, but forcing a Master's degree level studies into practical use where it doesn't naturally follow, mostly results in studies of 'how come bread always falls butter-side down' kind, and that, on Polish unis, is considered waste of time.
Master's degree is regarded as a basic 'outcome' of getting higher education in Poland (graduating with a license, although now actually possible, is still widely considered giving up half way). It's quite possibly the reason why any serious studies begin above that level, unless we're talking about some specialist, unpopulated divisions where every pair of hands counts. (I had a friend in astronomy division who started helping with her professors' studies as soon as she got the vibe of how to handle observatory equipment, because it needed constant attention and they had too little PhDs to manage)