As a general rule no you shouldn't delay PC. That being said it really depends on the fight duration and how many times you can use your CDs.
Myt Butcher for example last for 3:40 to 4:10, this means that you'll be able to use PC 3 times and shards 2 times so you can hold the second shards (and MI if you picked it) to line it up with the 3rd PC.
When you prepare for a fight, look at the length and plan your CDs accordingly.
I generally hold PC for AP, not for trinket procs. IF they line up, then thats awesome. Also if you're using Supernova, once you use it twice, you wait for 1 charge, use that then pool the next 2, and your PC should be off cd (with AP coming up 5-10 sec after)