One of the reason I like LR is that I shoot nothing but RAW, and don't like the idea of converting my RAW files to any other format (LR works non-destructively).
I started digital in late 2006, and continue to advance in my PP skills. I've gone over most of my old images and re-processed them - fortunately all my images are the original RAW files. Some people keep both the original RAW and the file converted to DNG, or whatever other format, but this takes more HDD capacity.
A feature of LR I frequently use is to create duplicate images so as to compare different processing; LR doesn't really create another RAW file, but creates a separate side-car file. So I can have multiple PP versions of one file and use very little extra HSS space.