If you want your Mac to run buttery smooth, you need to make sure that you there is at least 10 percent of your storage free always. If you are running out of space it can badly hamper your computing power (in which case you might be tempted to get a Mi Notebook Air).
For MacOS Sierra
For macOS Sierra Apple users there is new Optimized Storage feature that can help you delete your old files or also help in moving things you don’t need on your Mac over to the cloud.
For its access you need to click the Apple logo on your screen and choose the option About This Mac.
Next tap on the Storage tab to show you how much storage you have available and how it is used
The manage button will open another pane where in you have will be given four options which are Store in iCloud, Optimize Storage, Empty Trash Automatically, and Reduce Clutter.
There will also be a number of tabs present on the left side of the window for all your Applications, Documents, GarageBand, iCloud Drive, Mail, Photos and Trash.
The first option will delete TV shows or films that you’ve watched and it will also remove email attachments. You don’t need to be afraid of losing any of these things as emails will still be stored on the iCloud server anyway.
The second option will review the content of your Mac and proceed to delete your older documents. Clicking on this option will take you to a pane that shows Large Files, Downloads and a File Browser. The magnifying glass icon present near will preview files, and click on the x to delete them.
Remove photos to free up hard drive space
It may prove to be beneficial some times to delete some of the extra unneeded shots. If you haven’t been doing this from time to time it time now start, even if you intend to just copy over the entire Photo library to your external drive or if you start using the iCloud Photo Library.
Crop iTunes to recover storage space on your Mac
The iTunes library is another place for re-claiming disk space. You have some options here. One of it is that you can copy the entirety of your Music directory to an external hard drive and point it to iTunes from the preferences. That would be great if your Mac is a desktop model, but it’s not very ideal if it’s a notebook.
Remove files from your Downloads folder
There may also be large files on your Downloads folder which you know longer need. If you download large number of PDFs, images, or disk image files and don’t reduce on the Downloads regularly, it’s going to be probably full of stuff you don’t need.
Quit apps that are running in the background to free up space
Closing or quitting of apps that have remained open for many several days or more, and also restarting your Mac completely on a habitual basis will help clear up disk space.