EventPayload user type says fields ending in "_id" will be used to attribute the event to a particular user — what does that mean?

[evanrs]

The type doc for the Inngest JS client says that fields on user ending in the affix "_id" will be used to attribute the event to a particular user
https://github.com/inngest/inngest-js/blame/main/packages/inngest/src/types.ts#L306

What does this mean?