Why to use Photoshop?
Light room is a powerful photo correction tool, but it still can’t replace power of Photoshop for photo editing.
Here is an example of a photograph edited with Lightroom only and then processed in the Photoshop. I will use a photograph from the City of Lights, beautiful Paris. You can noticed that color cast was totally eliminated contrast improved. As a result the colors pops up on the final photograph.
Check before and after.
I also like to check tonal contrast of a photograph. To do so we need to eliminate color clutter, by converting photograph to Black and White. There multiple ways to do that in Photoshop or you can do that in Lightroom.