I have always recommended maxing out the RAM and although Mavericks and Yosemite have a very different memory management scheme, I see no reason to change that recommendation. The memory management scheme used in OS X changed radically with the advent of memory compression in Mavericks. Regardless of how much RAM you have, the memory manager is now designed to keep RAM maxed out or nearly so. As DK said, the whole idea is to minimize any necessity of pageouts to or pageins from the swapfile(s) on the HD or SSD. (Technically some of the swapfile space is not on the HD or SSD but in compressed memory in RAM
)
SIDE NOTE; I used to have a web page pictorially describing the relationship between virtual memory, RAM, and swapfiles and how to interpret the information displayed in Activity Monitor that according to the number of hits it got was pretty widely used. Unfortunately it was rendered hopelessly outdated and in some aspects incorrect with the release of Mavericks. One of these days I am going to redo that page adding in all the changes that memory compression have brought about, but I will probably have to invest in some animation software to make it easily understood.
