If the value in the parentheses is 0 (zero) then OS X is not making instantaneous use of VM which means you have adequate physical RAM for the system with the applications you have loaded. If you open the Terminal and run the top command at the prompt you will find information reported on Pageins () and Pageouts (). If you are really in need of more RAM that would be indicated by how frequently the system uses VM.
The Swap figure represents an estimate of the total amount of swap space required for VM if used, but does not necessarily indicate the actual size of the existing swap file. This will change as applications are opened and closed or change from active to inactive status.
The amount of available RAM for applications is the sum of Free RAM and Inactive RAM. Using Activity Monitor to read System Memory & determine how much RAM is used There are still indicators of when you are over-using the memory you have. Both Mavericks and more so in Yosemite, the OS takes command of as much memory as possible in order to better manage the needs of all the running processes. You should be aware that what others tell about memory usage in Mavericks or Yosemite or any other version of OS X is usually misinformation. If you believe you are using too much RAM by opening too many applications, then quit the ones you don't need to use at the moment.
