People often panic when their computer's resources seem to be maxed out. While CPUs and hard disks may suffer from high usage, a low amount of RAM doesn't necessarily slow down your computer .
If you have a lot of programs open, your computer is running slowly and your RAM is maxed out, performance can suffer. In those circumstances, your computer will start caching to disk instead of RAM, which will slow you down since reading and writing to disk takes longer. If this happens to you regularly, you may need more RAM.
However, high RAM utilisation on its own isn't necessarily a problem. Yyour RAM may still appear to be in full use even if your computer is running just fine. Often your computer is simply filling your RAM up with cache files. How-To Geek explains:
Whether your RAM is full of cached files or completely empty, it's all available for programs that really need it. Cached data in your RAM is marked as low-priority, and it's instantly discarded as soon as the memory is needed for something else. Because this data can be instantly discarded when necessary, there's no disadvantage to using the RAM for cache. (The one potential disadvantage is users who don't understand what's going on becoming confused.)
Empty RAM is useless. It's not any faster for the computer to write data to empty RAM, nor does empty RAM use less power. In fact, assuming you're launching a program that may already be present in your RAM's file cache, programs will load much faster when your RAM is used rather than when it's empty.
The lesson? Don't worry if your RAM appears to be full unless your computer is actually running slow. For an in-depth look at the subject, read the full post over on How-To Geek.