Placenta question??

So I had my placenta taken out forcibly by the IMPATIENT on call doctor with my last child. Now knowing the risks and dangers of doing that, I'm nervous that with my next baby they might tell me they have to out of emergency.

Can anyone tell me if there a legit reason they should take it out themselves and what the reasons are? And should they always wait 30 minutes no matter what before taking it out themselves?