What is Autovacuum?
Autovacuum is Automatic Vacuuming. GC for database tables.
VACUUM -- garbage-collect and optionally analyze a database
UPDATE records, your table will have Live Tuples and Dead Tuples.1
You 100% want autovaccum ON. You want it to run frequently for small chunk of your database tables.
When you migrate a large database to a new database, you will see high CPU usage.
The autovacuum can be configured per-table basis.