Note: This is an annoyance, not an "OMG! M$ SUX0RS!" moment. For those DVDs I have with which it is annoying or a pain to use the 'My Movies' interface (i.e., multi-disc sets, particularly of TV shows ...
There's something inside your PC that's quietly gobbling up space. It's not evil. But just a hidden Windows folder that can quietly grow for years, sometimes reaching 30–50GB. It does so stealthily ...
The Windows system consists of thousands of files. Many of them have strange names, others have extensions that most users have never seen before. Normally you do not need to worry about these files.