(See this forum thread.) Granting anything more would, in fact, slow down both the host and client, but I have no problem assigning 8 GB of RAM to a VM in Fusion before really committing to Parallels, I'd like to know the rationale behind such a recommendation (and no, the Parallels forums don't shine satisfactory light on the subject, at least from what I've been able to dig up). I'm wondering about the baffling Parallels recommendation (when configuring a VM) that there is a maximum cap of 4 GB of RAM for a VM with Parallels (indeed, it recommends 1.5 GB for Windows 8).
I'm a VMware Fusion user and am trying out Parallels since VMware has some quirks that are annoying on Mountain Lion on a retina MacBook Pro (16 GB RAM).