In my experience, using pconnect doesn’t hurt, but it doesn’t necessarily help.
Years ago users would complain about pconnect not working, and in tests I found that in fact it did not work. At all. Every time you called it, it made a new connection.
However, I think the PHP people may have fixed that bug (it was quite a while ago). It’s definitely advantageous to use them on our system since we charge for excessive MySQL usage (and connections are particlularly computationally expensive).
They may not save any connections, but they won’t hurt.