To elaborate, you only want to bond the neutral and ground at the service entrance. That means no bonding in subpanels, branch circuit infrastructure, or load-related equipment. Bonding at other places reduces the effectiveness of the safety ground, as it creates ground loops that enable current to flow on the safety ground. This increases the possibility that safety ground's potential will rise at the point of use (reducing its effectiveness of a safety measure), and also reduces the ground's value as a reference.

Why does this happen? It's a simple matter of current division. The old adage "electricity always follows the path of least resistance" is actually quite inaccurate. Think back to fundamentals of circuits. When you have a current that has a choice of two paths to follow (neutral and ground in this case), it does not simply choose the lower resistance path. It is true that more current flows through the lower resistance path, but a smaller amount still flows through the higher resistance path. It is a false assumption that either the safety ground or the neutral has 0 ohm resistance.

--Sasha Jevtic