[simias]

Lossless means lossless, i.e. you have no loss of information. The decompressed video is exactly what you had when you started. It's PNG (lossless) vs. JPG (lossy) or FLAC (lossless) vs. MP3 (lossy).

Of course lossless compression is typically a lot less compact than lossy alternatives (the article mentions a 1/2 compression ration, which is not much compared to lossy video codecs) but it means you're not degrading your video at all, you just have additional processing.

Note that some algorithms these days claim to be "visually lossless" which is mainly a marketing gimmick which means that it's lossy but you wouldn't be able to tell the difference with the naked eye in normal conditions (TICO claims that for instance).