Rod: Stick to tuning the piano. Leave the playing to the experts.
One of the reasons APS has detractors is that engine monitors and pilot education have exposed the variable quality of engine manufacture and maintenance.
The effort and cost it takes to get F/A mixtures balanced across cylinders shows how poorly balanced it is off the production line. Many new, certified and quality stamped cylinders need to be set up properly by the few remaining competent experts before fitment. Bushings made of cheese. Spark plug suppressors made of unicorn farts...
I can tell, on the first flight after maintenance, whether timing advance has been fiddled with and set correctly. Some engineers don’t like it when you say: “As a consequence of a change in CHTs and and in-air mag check, I can tell that you’ve advanced the timing on right magneto too far.”
Blocked injectors usually happen just after maintenance. Engineers don’t like it when you say: “The injector on 4 is blocked as a consequence of contamination introduced during your maintenance.”