That's a good question, and one that often comes up when dealing with new construction or remodels involving metal fixture mounting hardware. Here's a breakdown of why grounding might be considered, and why it's often not required in your situation, along with some considerations

Why Grounding Might Be Considered (And Why It's Often Not Required)
Safety First

The primary reason for grounding metal electrical enclosures and components is safety. Grounding provides a low-resistance path for fault current to flow back to the source, tripping the breaker and preventing a potential shock hazard if a live wire comes into contact with the metal.

Code Requirements

The National Electrical Code (NEC) is the authority here. Generally, metal electrical enclosures must be grounded.

But... Contact Matters

You're right in pointing out that your rough-in plates often don't make substantial contact with anything else. This is the key. If the metal rough-in plate is isolated and not likely to become energized through contact with a fault current, it is often not required to be grounded.
Your Specific Situation (Wafer Lights in Older Homes)

Given that you're dealing with wafer lights and rough-in plates designed primarily for positioning, here are the factors that suggest grounding is likely not required:1. Isolation

Wafer light rough-in plates are typically designed to be isolated from the ceiling structure. They're usually held in place with clips or tabs, creating an air gap.2.

Intended Function

These plates are primarily positioning aids. They aren't serving as a primary electrical enclosure.3.

Modern Wafer Light Design

Modern wafer lights are designed with safety in mind. They often have double-insulated construction and internal fault protection. The light fixture itself should be properly grounded through its wiring connection.4.

Likelihood of Contact with Energized Parts

The wafer light's wiring connections are contained within the light fixture itself and should not be in direct contact with the rough-in plate.

NEC Considerations NEC 250.4(A)(1)

"Electrical equipment and wiring shall be installed in a neat and workmanlike manner... The electrical equipment shall be free from short circuits and from grounds other than those required or permitted by this Code." The "required or permitted by this Code" is the key phrase. You only need to ground something if the NEC explicitly requires it.

NEC 250.8(A)

Addresses connection of grounding and bonding equipment.

NEC 250.110

Covers equipment required to be grounded. Read through these sections carefully and consider how they apply to your situation.

Local Amendments

Keep in mind that your local jurisdiction may have amendments to the NEC that could be more stringent.

Recommendations and Best Practices1. Check with Your Local Inspector

The best course of action is to contact your local electrical inspector. They are the ultimate authority and can provide definitive guidance based on local codes and interpretations. Explain the situation and ask for their opinion.2.

Review the Wafer Light Instructions

The manufacturer's instructions may have specific grounding requirements for the rough-in plate or the fixture itself.3.

Err on the Side of Caution

If you're uncertain and grounding is easy to do (e.g., a nearby ground wire is accessible), it's generally better to ground the plate. However, do not create a ground connection where it is not designed for (e.g., forcing a wire into a hole).4.

Proper Connections

If you do ground the plate, use an approved grounding connector (e.g., a grounding clip or screw) that is specifically designed for making a secure electrical connection.5.

Maintain Isolation

Make sure the rough-in plate does not inadvertently make contact with other metal parts of the building structure. If contact is unavoidable, grounding might become more important.

In Summary

While grounding is crucial for electrical safety, the isolated nature and positioning-only function of wafer light rough-in plates often mean they are not required to be grounded. However, the final decision rests with your local electrical inspector.* Review the NEC, consult the manufacturer's instructions, and, most importantly, talk to your inspector. Flag for review