John is getting a message that he's running out of drive space, but he has over 200GB of "other." Where is all that space going? Leo advises using a great program called Disc Inventory X. It will tell him exactly what the storage files are and it'll be color coded for ease of use.
Leo suspects a lot of it is cache and temp files that he doesn't need. Here's a good article on iMore that shows step by step how to clean it all out. It recommends Daisy Disc as a utility. Another good application is OnyX.