Any channels you need to share data via the registry should use the same DevID. Typically, I would think an upgrade would fall into that category.
Additionally, since the registry space is allocated based on DevID, anything stored in the registry will remain there until all channels with the same DevID are removed (or it's explicitly deleted). You're also limited to 16k across all channels using the same DevID.
So, related channels should use the same DevID. Unrelated channels should not.
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