From what I understand Chromium has a blacklist of particular WebGL features for particular devices. This means that some WebGL features may cause potential issues sometimes.
When you have it enabled chromium has to check against the blacklist everytime your game tries to execute some WebGL feature.
Now if you ignore the gpu blacklist, then such features will be treated by hardware acceleration.
But this is just how I understand it and it is still not clear for me (I may be wrong). Hard to find any detailed information how it works and what it exactly does.
Still, thanks for the information.