If you are running a version of the operating system older than macOS Sierra, you can manually wade through your drive tossing old files or get a third-party cleaning app to sweep up for you. Click the X next to each file to delete it. To see what the Mac considers “clutter,” click the Review Files button and go through the lists of files deemed large, old or unnecessary. Using the Reduce Clutter feature is another way to find big files hogging drive space and remove them. (In macOS Sierra and later, the system also automatically dumps duplicate Safari downloads, cache files, logs and other unneeded files.) The Empty Trash Automatically setting permanently deletes files that have been living in the Mac’s trash for longer than 30 days.

The setting also changes the Mail program’s behavior regarding file attachments to retrieve only recent files - or only those that came with messages you have opened. Enabling the Optimize Storage feature dumps iTunes videos you have already watched, but you can download them again later.

How to reduce mac hard drive space