Currently we are keeping all post revisions from auto-save for ever. I experimented on a test instance with GPI prod data.

1. Exported the DB and checked its size: 226M
2. Delete all revisions except the ones save in the last week
3. Exported DB again and checked its size: 134M

The command I run in the experiment:
wp db query < revisions.sql

and the query:
DELETE FROM wp_posts WHERE post_type = 'revision' AND post_modified < NOW() - INTERVAL 1 WEEK;

So besides limiting revisions we can do a clean up.

Relevant Documentation