Prefstats is an old extension which has been unused for years and is now decomissioned (see T134441). However, its database tables (named prefstats) still exist on the production cluster, or at least the analytics store replicas, despite having no updates since 2012:
select max(ps_start), max(ps_end) from enwiki.prefstats; max(ps_start) max(ps_end) 20120321190136 20120321195103
These tables can all be dropped. I can confirm the Editing department does not need the data, since it's old and since we have very similar data in the PrefUpdate event logs. I'm filing this because my impression is that the DBAs prefer to delete unneeded tables; personally, I would be fine if they were not deleted too.
The table on enwiki has about 3 M rows.
Deletion progress (backups: T154490#4107502):
- s8 - table not present