I get a lot of questions asking about organizing Lightroom catalogs and also clearing up space on internal hard drives and moving to an external drive.
There is also some confusing topics around mobile editing, moving files to a laptop to edit and then moving them back.
Here are some videos that I've worked up that will show you these procedures and hopefully clear up some of the confusion.
I also have a detailed post explaining some catalog theories and management on The Business of Boudoir http://thebusinessofboudoir.com/clean-that-mess-organize-lightroom
Let me know if you have any questions