Well you'll obviously need to connect to the database somehow.
Personally, if I know there is a connection to my database already (I also have a class to connect, query etc...) I will just global the connection, if not create it.
If I am unsure, I will use isset() to determine whether or not there is a connection.
Creating new connections to run concurrently with ones that already exist seems pointless to me. You're just making multiple connections for no reason, thus will slow down your script.
Up to you though...