That's backwards once useage is past a certain point. Opening new programs with high memory utilization already occuring will require more memory INCREASING HDD useage as the system has to resort to the swap files to meet memory requirements.
True - What's needed in order to maximize both sides of that particular situation is some intelligence in the OS which can keep track of which programs the user is likely to launch; and at what days/times. From there, it's simple to manage what is cached and when.
I wonder what OS can do that??