NFD

Caution: when L3 objects such as ndn::Interest are passed via a ring buffer, attached ndn::Tag are passed along and could cause undesired effects. DummyClientFace and TopologyTester both encode the packet into L2 wire format and then decode again.
While it's desirable to avoid encoding-decoding, if side effects are detected, passing around L2 wire format is still faster than going through sockets.

Can you give an example of a Tag that can cause unwanted effects?

It’s more about two NDN entities (nodes or apps) updating tags on the same TagHost. They can conflict.
A specific example:

A-B-C
  |
  D

A’s face 3001 is B, B’s face 3001 is C, B’s FIB entry point to D.

A receives an Interest with NextHopFaceId=3001 so it forwards the Interest to B. B normally should not see NextHopFaceId so it should forward the Interest to D. However, if Interest instance is passed around, B would incorrectly forward the Interest to C.

Can't we simply remove all tags from the packet instead of re-encoding?

No, because the originating node may still need those tags.

I can think about an alternative: copy the L3 packet object, then clear all tags on the copy. This should work because tags are stored on L3 instance, while underlying Block has copy-on-write semantics.

Why are you talking about multiple nodes now? Your answer seems completely off-topic.

Why are you talking about multiple nodes now?

I cannot speak for InternalFace's use case. The example is from TopologyTester.