On /r/consulting people talk about PIPs fairly often so look there if you want a variety of situations and answers. The general thought there is if you are being put on a PIP look for another job as the company will have a reason to instantly fire you and it will hang over your head forever.

I was on one where I passed. I thought it was quite demeaning how my manager, the GM and HR waved their finger at me out of the blue as if they were angry parents who felt they needed to scorn someone. I didn't truly understand what I was in trouble for ESPECIALLY how much they emphasized "don't try to rope others into this." I didn't say anything in the meeting other than I apologize for this performance and I agree to the PIP ... In the next meeting my manager said my silence was noted by HR as a lack of empathy and they were close to escalating to instant firing at that stage. I wasn't exactly sure what I was expected to do but I attended all necessary meetings and improved my performance and was taken off the PIP. At this stage I'd gone through the recruitment process with other roles and resigned shortly after.

EDIT: As OP is a manager they might want to know how they can manage poor performance better. The worst manager's I've had have skipped weekly/monthly meetings with me then after three months exploded about certain work which was mentioned in a passing conversation not being completed. If you are considering escalating performance issues to HR I think it is good practice to ensure the staff member is notified after the meeting in email that you've talked to them about performance.