I actually have multiple runtimes as I run multiple versions of Poser (Poser 7 Pro - Poser 2014 Pro). My oldest runtime dates back to Poser 4, and this is where almost all content that works in Poser 7 or earlier now goes. I have a separate Runtime for content needing Poser 9/2012, and a third for 2014. If I ever get a system to run Poser 11 this will likely be yet another runtime. I also have a separate development runtime, a Beta runtime, and an area I use to install new content with multiple temporary runtimes broken down by Figure, Sets, Vehicles, Aircraft, Animals, Creatures, Robots, etc... I use these to edit the content in the characters sub folder and rearrange it to my liking before adding it to my main runtimes (this way all of V4's clothes are in a V4 folder for example). Sadly with my oldest runtime I was not this prudent and I have a lot of items installed that I no longer know which specific figure they are for...the stores are gone, the product pages lost...and so it's guesswork on some things now.
My biggest recommendation to anyone just getting started would be to take a bit to figure out an organization system that works for you for content and start on it early. weather it is to use seperate external runtimes for scenes, plants, vehicles, or to move it around inside your runtime. If doing the later, be cautious, some items are not easily moved because of where they place the geometry for the figures. Ideally the geometry should be in the geometries folder and I never touch this, but some content, especially stuff from Smith Micro and the old CP store placed the geometry pretty much wherever they wanted, and if moved with brek the figure (unless you edit the CR2 to point at it - but this isn't for everyone).