It used to be you would always keep your negatives because creating a print loses some detail, and copying a print lose more, and each copy of a copy compounds the issue.
In the digital world we don’t have negatives and prints, but RAW files and JPEGs are much the same.
Creating JPEG files is very similar to making a print from the RAW file which is like your untouched negative; some data is dumped and the image is compressed. The small artifacts and errors are usually too small to be noticed but if you re-edit the JPEG and re-save it (compressing it again) those artifacts and errors will grow and be magnified. The same error compounding as when you make a copy of a copy of a copy.
This video shows what happens when an image is re-saved and compressed on top of itself as a JPEG 500 times.
Moral of the story:
Save your RAW files (negatives) untouched, and export new JPEG copies off of them for the edits you make. If you want to make new edits or change the photo, create a new JPEG using the RAW file as the base so you don’t perpetuate any errors created in the last JPEG save.
Luckily this is the standard operating procedure of Lightroom. Your original file is untouched and Lightroom shows what your edits will look like; but a copy of those edits doesn’t exist until you export the image creating a new JPEG. Even if you delete Lightroom and it’s catalog you’ll still have your folder full of untouched RAW negatives you can rebuild from.