In the early days of digital photography (before Lightroom was born) photographers were predominantly using Photoshop to edit their files. Many of us became really comfortable with Adobe Bridge and that is where we did a lot of batch processing and organizing of our files and then easily sent our files to Photoshop for additional editing.
However, for anyone that was using this workflow it could really bog down your computer and your workflow because Photoshop can tend to be a RAM hog. Thankfully about 12 years ago Adobe came out with their beta version of Lightroom and about 10 years ago we were all pretty happy with what the newer versions of Lightroom had to offer.
As it stands most of us can do 85% of our editing in Lightroom but we still need some Photoshop skills to really polish our images. That being said, gone are the days of my intensive Photoshop classes that tried to give you an in depth working knowledge of the program. What I have found is that unless you are working in the program all the time the knowledge gets lost.
These days I offer Photoshop classes that are very specific with step by step instruction with skills that 'every photographer should know how to do'. Armed with this bag of tricks you can clean up, fine tune and make all of your images the best they can be. The truth is there are just certain things like retouching or other creative things that cannot be accomplished in Lightroom.
The first class is "Essentials". This class teaches you how to get from Lightroom to Photoshop, the work space, layers, layer masking and adjustment layers. This class is recommended for anyone wanting to learn basics of the program.
The second class is "Retouching". This class only teaches you retouching of files, removing things, adding things, portrait retouching, body sculpting, adding more interesting skies etc.
The third class is "Collages and Composites". This class teaches combing images, for graphical purposes, brochures, posters, text, graphics, gradients etc-more creative work/mixed media.
These class will give you the right amount of skills without totally overwhelming you with a lot of information that you may not need or use.