Playpen pros and cons please

[FunkyCherry]

My parents have offered to buy me a playpen.
I don't want them to waste their money, so before accepting, I'd like to know how much use you think they are.
What are your experiences?

We introduced DD to a playpen at about 6 months. She was starting to try to roll and i wanted another way of keeing her a bit more separate from the dog. She HATED it! We kept it up for about a year, and used it when we needed to then it came down when we moved house.
Thinking hoping it'll get more use with DD2 when she arrives, as she'll go in it pretty much from birth so DD1 can charge about and I know she won't accidently step on the baby.
They definitely have their uses.

I love our travel cot which doubles as a play pen. We call it the baby jail. But honestly, once they start moving around it is great to stick them in there when you need to pee/answer door/make tea etc. Much quicker than strapping them into a highchair or whatever, and less restrictive.

We recently turned it into a sort of den by putting it on its side. DS is nearly 11 months.