Some photographers prefer to convert their original proprietary raw files (ARW, NEF, CR2 etc) into DNG files straightaway upon importing to Lightroom from a camera or later, using Adobe DNG Converter.
If you are using DNG to store your images, you can still compress them in Rawsie and benefit from even smaller file size, but this will not work in this cases:
➊ Files coming from unsupported cameras (please see camera support list) will not be compressible in DNG format either.
➋ DNG files that were lossy compressed in-camera or in other software (e.g. in Adobe DNG Converter) will not be compressible. For example don't switch on this setting in Adobe DNG Converter: Or don't turn on this setting in Adobe Lightroom: ➌ Files falling under brand or camera specific limitations outlined here will to be compressible in Rawsie..