Google Chrome likes to use memory and give your processor a good workout if you keep a handful (or more) tabs open on a regular basis. This can have a negative impact on the speed of your computer, and certainly the life of your laptop's battery. The Great Suspender solves that problem by shutting those tabs down when they are not in use.
As pictured above, you can see The Great Suspender offers a number of manual options: suspend this tab, suspend all tabs, reload all tabs and settings. The settings section is where things become particularly useful, because you can automatically suspend tabs after a set number of minutes or hours. This way, they won't eat up memory and add to Chrome's CPU usage in any way until you go back to them and load the page back up.
It would be awesome if Chrome had this feature by default, but this third-party extension does the job nicely for now.