the insert module isn't cleaning up the data in the table 'content_node_field_instance' after you remove imagecache styles from the configuration in the fields/content types.
say you remove 10 styles from the list of insert - they never leave the data in the table.
if you do this over and over, the table will get huge and the site slow.
it's also not updating accordingly to imagecache preset changes.
say you add 10 styles to the list of insert, then decide the rename or delete those styles in imagecache.
the config for the styles vanishes, but they remain in the data, and can't be removed from within the UI.