In QGIS I just used the tool "cliprasterbymasklayer", which produces a new raster layer as output and gives me the option to "create an alpha band". I read that the alpha band represents the transparency but I don't see any use case. Even if I don't choose this option I can make the new raster more transparent. If I check the option the new raster is lighter and has 0 as lowest value.
I was just wondering about a situation in which that could be practical. Any ideas or examples?