IF you apply parametric edits in LR, there's no damage. It's only textual data that describes an edit WHEN you export. As other's have said, at that point, saving out as a TIFF would make sense. Now keep in mind that IF you apply such edits in LR, but open that JPEG outside it (or ACR), those edits are not seen (they haven't been applied to the JPEG image data, it's just text at this point). So if you always keep the JPEG's in LR and do further editing there and you export that new iteration as a TIFF, that's the best way to prevent further JPEG damage (cause you now have a TIFF). But if you intent to keep the JPEG's in LR forever, might as well keep them as JPEG's.