max_wal_senders

I've been thinking about the max_wal_senders parameter lately and wondering
if there is any harm in setting it too high. I'm wondering if I should try
to shave a few senders off, perhaps to match my logical replicas + 1,
instead of just leaving it at the default of 10. Or vice-versa, can
clients use more than one sender if they are available? Would increasing
it result in lower latency? The documentation is a little vague.

The documentation mentions an orphaned connection slot that may take a
while to time out. How can I tell if I have any of those? I was looking
for a `pg_wal_slots` table similar to the `pg_replication_slots` table, but
don't see anything obvious in the catalog.