My experience with P charting has not been good. The first hurdle is that you are charting defects. If there are only one or two of these going on, and there is visible activity to "fix" the process, it should not be a problem. Unfortunately, a couple of years ago we had more than a couple of these charts, which the engineers were using in weekly meetings to demonstrate "sameness" in their areas of responsiblity. What was lost on them was the operators reporting the percent defective began to get used to defects being OK, and some took this to other departments after they bid or were transferred. It became a pervasive problem. Our customers do not stand for defects, and we had already set up 100% inspection for these parts to protect the customer. I could get information just as quickly from the inspector's time cards each day.
Prior to QS9000 implementation, I recall two instances where customer auditors found P charts more than 5 months old, and they obviously looked for corrective action. All they saw was 100% inspection.
I can certainly see benefits for utilizing P charts, but I am tentative when someone wants to use one for more than a couple of days or weeks.
BTW, we are high volume component and assembly supplier to Ford, GM, Japan.