Free memory is memory that isn't doing anything. It's no better than memory you don't have. If you're thinking "I want it free now so I can use it later", well, "later" never comes. Whenever it is, it's always now. Now is always later than some time in the past. So why not use it now? It's not like using it now means you can't use it later. You can use it now and also use it later. You don't have to choose.
Making RAM free takes effort, effort that the system just has to undo in order to use that RAM. Like most modern operating systems, OSX can transition RAM directly from one use to another in a single operation, which is much more efficient than two operations to do the same thing. So there is no reason to do this.
For some reason, people have this obsession with making as much RAM as possible free. This means making the system use as little RAM as possible. But this just makes the system slow. The whole point of RAM is to use it to make the system fast. If you want it to be free, take it out of the machine and leave it on a shelf.