Want to run more programs at the same time?
Memory is a great upgrade which in short allows you to run more programs and do more "things" at the same time. Memory helps with video games and even video streaming services like Netflix and Plex. Memory also helps with overall performance but at the same time not like a solid state drive.
I currently recommend 6 - 8 GB of memory for starters. Anything under that can cause sever delays in software opening and performing.