install agent vs. WMI

I've always used WMI when adding nodes. The service account I created in AD on the domain was placed in the built-in Administrators group. Now, for auditing purposes, I'm instructed to remove that service account from the admin group and install the agent so that it can use the local account for monitoring. 

What are the pros and cons of using the agents? I understand it requires an open port to the internet?