Need More Space On Your Mac?

Try These Tips 

 “Your startup disk is almost full. You need to make more space available on your startup disk by deleting files.”
If you are a Mac user and you haven’t run into this particular error message yet, chances are you will eventually. If there is less than 20 GB free on your hard drive, your computer will start to slow down. With less than 10 GB, you will be forced to quite running applications until more space is cleared.
Sometimes there’s an easy fix for a full disk—emptying your trash, clearing your cache, moving that three-hour video of your sister’s dance recital to an external hard drive, etc.
Detecting The Source
In other cases, clearing space requires a little detective work. Start by checking out your system information, available by selecting About This Mac, clicking on More Information, and checking out the storage tab. If you can see that audio or video are eating up your hard drive, the best option is moving songs and videos to the cloud or to some kind of external storage device.

The storage data for a relatively clean disk

If apps are the problem, think about removing applications you don’t use regularly.
The Obvious, First
The obvious choices are things that you’ve downloaded independently, but it’s worth looking at the default apps that came with your computer as well, i.e., Garage Band, iMovie, and temporary trial software that came automatically loaded.
Removing applications completely on a Mac requires a little creativity. Simply dragging the file from the applications folder to the trash will leave behind a lot of the associated files.
Use An Uninstaller
To make sure files are completely and totally deleted, use an uninstaller like Amnesia or AppTrap, or follow these instructions from MacRumors for manually deleting applications.
If a giant chunk of your storage space is taken up by the enigmatic yellow “other” bar (that was the case for me), look for file types that don’t fall into the named categories. Examples include email messages, zip files, and virtualized operating systems.
Helpful Tools
It may still not be clear what is hogging space on your Mac. If you’re still stumped, try downloading a tool to help visualize the files taking up your hard drive. Disk Inventory X worked well for me, but Grand Perspective and Daisy Disk are equally good options.

Disk Inventory X hard drive visualization

I can tell you from personal experience that cleaning out a full hard drive can make a serious difference in your computer’s performance.