The documentation of poll() did not explain this in detail. While polling on an fd, when should one POLLIN and when should one use POLLPRI? Any insights will be useful.
I always use both of them, that's possible since they're bitmasks (so you can use POLLIN | POLLPRI).
The priority entries are for information that's considered more important than regular information. Ideally, you'd ask for both types and then check/process the priority ones first.