Problem/Motivation
#2976334: Allow non-reusable blocks for placement in the Layout Builder
#2957425: Allow the inline creation of non-reusable Custom Blocks in the layout builder
Allow adding non-reusable blocks through Layout Builder which means that this will allowing adding individual blocks for every content entity that supports layouts.
This will mean a site could easily have thousands of custom blocks.
Currently if a site had thousands of custom blocks this would cause many block would cause performance problems on Block UI page.
This should not be the case with non-reusable blocks because \Drupal\block_content\Plugin\Derivative\BlockContent::getDerivativeDefinitions() will not create blocks for non-reusable blocks.
But we should use the patch in #2976334: Allow non-reusable blocks for placement in the Layout Builder to produce 1000s blocks and profile this.
We can patch files here to do this. But since this won't produce patch that should get committed I suggest anyone who works on this issue should also get commit credit on #2976334
Testing
Use: https://github.com/tedbow/blocks_profiler
Follow the instructions on the README.md for that project.
Comment with results.
Remaining tasks
Gets some people to test and confirm