Short answer – it doesn’t mean anything. Read on for the longer answer:
What is bottlenecking?
The concept of bottlenecking is that a program will only run as fast as the slowest component that it uses in the computer. When you upgrade a component, the program will speed up only as far as the next-slowest component.
A CPU (processor chip) bottlenecking a GPU (video card) would mean that the GPU is so powerful that the game play frame rate is being held back by a CPU that can’t keep up – and a more powerful CPU would result in an increase of frame rate up to the GPU’s capability.
In practice this almost never happens, except in scenarios where a $50 CPU is paired with a $400 GPU.
Assumptions:
We will assume that the machine has enough RAM, hard drive space and that the CPU and GPU are roughly the same age. If the machine has under 4 GB of RAM, or a hard drive that is almost full or having speed issues, then these problems must be addressed first before we can discuss GPU and CPU performance.
The reason:
Programs do not use all components of the machine equally. For most games, performance is heavily dependent on the GPU. The CPU plays a role, but as long as the CPU is at least adequate, the video card GPU performance determines up to 90% of the frame rate capability of the machine.
This means that for most games, any four core or higher AMD FX- or any four core Intel i5 or four core/8 hyperthread i7 CPU is going to keep up — even with a high end card like the Radeon HD7970. Even a dual core i3 at a good clock rate will perform well on games that don’t multithread heavily. There will be a tiny difference in performance, but in the test here
http://www.guru3d.com/article/radeon-hd-7970-cpu-scaling-performance-review/
all of the CPUs tested drove the top-end HD7970 card with playable frame rates even at the highest resolutions. There was a difference between CPUs in some tests, but really – are you going to quibble with the difference between 110 and 120 fps? Not if it costs $600 more to get a CPU that will give 5 – 10% increase in the already-fast framerates. It’s only when you get into dual high-end video cards (in Crossfire or SLI mode) that you would need to consider a higher end i7 CPU.
In this test, the Unreal Engine 3 at maximum settings was tested against a range of processors with the same Radeon HD 7970 video card.
http://www.techspot.com/review/507-mass-effect-3-performance-test/page5.html
The dual-core AMD Phenom II 3.3GHz got 88 fps, the six core Phenom at the same clock rate got 94 fps (illustrating that the engine is not using multiple cores effectively) while the top end i7-3960K at the same GHz got 127 fps. That is a $100 CPU up against a $1,000 CPU for an increase of 39 fps. In other words it took a 1,000% increase in price for a 44% increase in frame rate. For a $900 savings I’d be happy at only 88 fps, thanks. And the difference between the two would be less on a video card that cost less.
Have a look at the $120 AMD FX-4170 4 GHz at 98 FPS 833% jump in price for 29% improvement. CPU price does not scale well against game framerate performance increase.
What to get:
My processor of choice for all around power, 3D gaming and value for money is the third generation quad core Ivybridge i5-3xxx series, teamed with a Radeon HD7870 / HD7950 (or higher) or NVidia GTX580 / GTX670 (or higher) GPU, in around the $400 – $450 price point for the GPU.
The exception to this scenario is if you do a lot of media production (video, audio, graphics) or scientific or engineering applications as well as gaming, where the programs can aggressively use all 4 cores (8 virtual cores) of the i7, then get an Ivybridge i7. Most game programs do not effectively use all cores of the CPU, and most do not offload enough physics computation to the CPU to make a difference. If you have one of the rare games that does use an exceptionally high amount of CPU computation, then research the exceptions and buy accordingly.
Benchmarks:
http://www.tomshardware.com/reviews/gaming-cpu-review-overclock,3106-5.html
http://www.tomshardware.com/reviews/gaming-graphics-card-review,3107-7.html
What programs can use 4 cores effectively: https://computer-answers.ca/2012/computer-questions/q-is-a-quad-core-processor-better-than-a-dual-core/
How can I upgrade the video card in my machine? https://computer-answers.ca/2012/computer-questions/windows-questions/q-can-i-upgrade-the-video-card-in-my-machine/
Making a computer run faster https://computer-answers.ca/2011/computer-questions/windows-questions/q-how-can-i-make-my-machine-run-faster/