I have implemented this several times and it is very useful. Most recently for reFX, please see the reFX repo and consider implementing something similar. JUCE/juce_Component.cpp at reFX/develop · reFX/JUCE · GitHub
It’s two macros, START_PAINT/END_PAINT and if they aren’t defined then there is no performance impact at all.
It allows for some super cool visualizations like this that make it immediately obvious when you have painting performance issues:
