Tony, some information on saving different types of files.
Whenever you save a JPEG file the process is destructive because of the compression/decompression algorithms used.
TIFF files can be saved and reopened with NO degradation in image quality.
So, for your purposes, merely porting a TIFF image between applications, Lightroom to Photoshop, and back in your case, will have zero effect on image quality as long as the image is in 16-bit format and preferably with ProPhotoRGB embedded as the colourspace. I would never compress the image for this purpose either.
In the context, saving and exporting is the same thing since any changes made to the image in either application will be applied at a pixel level. If the result of any editing applied to the image in either application makes for a poor quality file that is another issue.
Nothing will be lost in the saving and porting and reopening of the file in another application.