The secret to understanding this is to forget the terms residential, commercial, etc. as electricity follows the same rules in any of those applications. (current still flows from one potential to another if there is a path to flow on)
The reason we ground and bond things together is to create a low impedance path so if there is a fault from an ungrounded conductor to conductive items it will allow for a high level of current to flow and cause operation of the overcurrent device.
The reason we only bond the grounded conductor to the grounding conductor at the source or first disconnecting means is to limit unintentional neutral current from flowing on all bonded objects in the electrical system. That current may be fairly harmless in a system in good condition, but when something happens to open a current path in something not intended to normally carry current - you will be subject to voltage across the points that became opened.
An example say we have a sub panel fed with metal raceway. Lets assume the neutral to can bonding jumper is installed. Lets assume there load on this neutral. With the bonding jumper installed that neutral curent has both the feeder neutral as well as the metal raceway as a path for current to flow through because they are bonded together not only at the source but at the load end of the feeder also. (and there may be other paths through other grounded objects that happen to be interconnected somehow) Lets just assume the feeder raceway is the only other path for now. What happens if the neutral comes loose for whatever reason on either end? The bonding jumper on the load end of the feeder still has a path to the neutral bus and that neutral current is all flowing in the raceway instead of the neutral conductor. This is not something you really want to happen. Now if the continuity of the raceway is interrupted you have a potential shock hazard.
Another issue is if you are loading your equipment grounding conductors with neutral current you are raising the potential to (earth) ground from your equipment grounding conductors and anything bonded to them because of voltage drop in those conductors. This will leave voltage between grounded metal objects and earth ground that can reach levels that will result in shock hazards, the more load the equipment ground conductors are carrying the higher the voltage drop will be.