When would upgrading the processor of the top of the line Macbook Pro make sense? As seen here, the top of the line MacBook Pro Retina  (with NVIDIA graphics card) has an option to upgrade the processor from 3.7 Ghz to 4.0Ghz via a "Turbo boost". 

I am generally wondering what kind of use would warrant this upgrade? 

More specifically, I am wondering if it would be of any benefit to web browsing with hundreds of tabs open, 3D rendering performance, or mass processing of images?
Turbo Boost is good for anything that uses a lot of CPU. It basically over clocks the CPU while it's needed and when it's not needed it doesn't run. 

It would help with anything that runs weighs down the CPU. I don't believe that it does anything with the graphics card (but I could be wrong).