The ray-traced 3d will make everything go much slower. If you have the right kind of NVIDIA GPU, AE can use the GPU to accelerate the 3d objects created by the ray-traced renderer.
That being said, the difference is the standard renderer is just 2.5d whereas the ray-traced renderer has actual depth and geometry including ray-traced reflections and shadows. It sounds like a neat feature, but it...it wasn't great. The AE team abandoned it and it is now considered obsolete for all intents and purposes. I never used the ray-traced renderer for any client projects. I poked around with it a bit and went, "Meh." There are better ways to get 3d in AE. For one thing, Element 3d, Zaxwerks 3d Invigorator, and Mettle's ShapeShifter are all faster to render and more fun to play with...I mean WORK with.
But even more interestingly, After Effects now comes with Cineware and a free Lite version of Cinema 4D. It is much more poweful and the interaction between AE and Cinema 4D is getting better with each new version. Here's a tutorial series on using it. The next version of AE and Cineware will allow you to send animated AE text straight into C4D for extrusion.