When and why you should clear inactive memory:
Inactive memory is a good thing that increases performance when apps need to re-use sections from memory. Like say when you relaunch an app you recently quit, in which case the app launches quicker than normal thanks to the inactive memory. But when most of your memory gets cluttered by inactive memory, even though there is free memory available, you'll see swap files kicking in (This is in cases where an app requests amounts of memory that exceeds the amount of free memory and includes a significant portion of the inactive memory). This slows the performance of your machine along with the fact that giving a portion of inactive memory instead of the free memory to an app is slower. If you are experiencing these issues, which appear mostly after running your machine without a restart for a while, you may consider cleaning the inactive memory to solve any performance issues you are having.