NOTE: Little clarification, this is not needed at all ,as memory is freed when required.
WHY IT MAY BE HELP-FULL: This clears the page-cache , dentires and inodes.
IT’S TRANSLATION : It may be that you are watching a movie or using a Virtual Machine , a resource hungry process has filled up your ram by caching data and the data needs to be continuously removed to make space for new data . This is managed by the kernel.
IF YOU STILL DON’T GET IT: Notice video in your movie hanging (not audio) while your ram gets cached Or your system running a bit slow ?
1) Stop the process consuming loads of memory. (Check System Monitor).
2) Open a terminal with root privileges .
4) echo 3 > /proc/sys/vm/drop_caches
5) echo 0 > /proc/sys/vm/drop_caches