Possible performance improvement: When a custom field is disabled, automatically uncheck the searchable box and remove the db index
Suppose you have about 20 fields in the custom group and they were almost all searchable (had the searchable box checked). Over time let's say half get disabled. The indexes are still in the db, and the searchable checkbox is meaningless because they don't appear anywhere anyway.
If the table is large, those indexes potentially cause trouble with no benefit.
If you go to re-enable, it's true it won't automatically re-check the searchable box and recreate the index, but there's no real harm, you just go back in and check the box.
An alternative to automatically doing this would be a status check: "The following fields are disabled but marked searchable. Consider making them unsearchable to improve performance on large databases."