If it were possible for programs to allocate caches that work like the filesystem cache, where old items get discarded automatically to make room for anything more important, then this would make sense. If you still have RAM available, it is actually detrimental to your system performance to free this data.
Programs load data into memory because memory is fast and your disk and the network are significantly slower hundreds or thousands of times slower, and pointlessly unloading the data from memory increases the risk of having to go back to the slower disk or network to retrieve it later. These are the same people who think they're increasing their computer's performance by turning off superfetch, etc.The problem with this perception is that it's completely stupid. Most people seem to have this mindset that using RAM is bad, and the more memory you have free and unused the faster your computer will be.