Each drawing answers a different question, so a useful twin draws on more than one. Plot plans and layout drawings show where things physically are, PFDs show the overall process at a high level and P&IDs show the detailed equipment, lines, valves and instruments that people actually isolate and work on.
For operations, the plot plan usually sets the physical layout and the P&IDs provide the equipment and connections that permits, isolations and procedures refer to. PFDs are useful for orientation but rarely detailed enough for day to day work, so starting with layouts and P&IDs covers what most field teams need.