How the limit moves
At low resolution and very high frame rates, the processor has to prepare an enormous number of frames per second, so the limit often sits there. Raise the resolution or the visual settings and the work per frame grows on the graphics card, which usually becomes the limit instead. The same pair of parts can therefore be processor limited in one game and graphics limited in another.
This is why the honest way to evaluate a build is per workload: name the game, the resolution and the target, then look at which side falls short. The forecast on this site does exactly that, and its compatibility notes point to the side that is constraining the result.
Reading utilisation correctly
High graphics card utilisation during a game is normally a good sign. It means the expensive part is being used. Low graphics utilisation with high frame rates usually means the processor or a frame rate cap is setting the pace, which may be entirely intentional.
Frame time consistency matters more than average frame rate for how a game feels. A build with a slightly lower average but far fewer dips is generally more pleasant than one with a higher average and frequent hitching.
Spending to fix the right limit
If the forecast says you miss your target because of the graphics card, more processor will not help, and the reverse is equally true. Money spent on the side that is not limiting produces almost nothing you can see.
There is also a legitimate decision to accept a limit. If a build reaches your target comfortably, removing a theoretical bottleneck is a purchase without a benefit. Spend where the target is actually missed, and leave the rest of the budget for the screen, storage or a better supply.
Measuring instead of guessing
The practical test takes ten minutes. Run the game you care about at your resolution and settings, watch whether the frame rate is steady, and note whether frame times spike during specific moments such as entering an area or loading assets.
Steady frame times with high graphics utilisation means the build is behaving as intended. Irregular spikes that appear during traversal or streaming point at memory capacity or storage rather than raw processing, and those are usually much cheaper to fix.
Write the result down before shopping. An upgrade justified by a measurement you made yourself is a very different purchase from one justified by a percentage from a website that has never seen your machine.
