There's no database clean up for dates unless an event is deleted (not trashed)- but there isn't much to worry about. The dates are stored in a separate table - so lots of dates does not clog up the
wp_posts table for instance.
With that in mind, only event queries would be effected even if the dates table became 'bloated' - but even then queries are either by ID or date and both are indexed. Also if, say, you have 50 events, recurring every week for the next 50 years, that's 50*52*50 = 130000 rows in the dates table - this is small fry for databases which should be able to handle millions of rows.
In short, the effect on performance should be negligible. Deleting an event will remove the dates from the table - but generally deleting stuff from databases doesn't improve performance.
An event 'clean up' is only really necessary if its a user-interface issue, but I think (I hope), EO handles events in a way that avoids that.