What it's referring to is the fact that when you check the "Enable Profile Corrections" box in the Lens Corrections panel, that doesn't guarantee that any lens corrections will be made. That's because sometimes Lightroom cannot automatically determine the lens that was used (it mostly does, but some lenses cause a problem). In that situation the user can manually find and select the correct lens profile, and the lens corrections are then applied. But if nothing else is done, the same problem will occur on the next image taken with that same lens....so the fix for that is, after manually selecting the lens, to use the "Save New Lens Profile Defaults" option. That then ensures that the manually selected profile will be automatically selected and used when the "Enable Profile Corrections" option is checked on images shot with that particular lens (either manually or via preset). Furthermore, those new lens profile defaults apply to the lens, not the specific camera/lens combination, i.e. use the same lens on a different camera body should still result in the correct lens profile being applied.