Quite often is not possible to use a regex which match all the variations as it would require a regex which is either too complex to maintain or not efficient.

For example a company might have several legal entities, each of them with a specific naming convetion for defining the corporate users. In this situation, rather retrieving the users from the LDAP (or different LDAP's) a regular expression is a more simple way to catch user activities, but when the naming convetion are too different, defining a regex could be a nightmare.

This would make sense for hostnames as well when managed by diffent infrastructure teams within the same organization.

By having the possibility of defijning a group of regex, this would simplyfy a lot the maintanance and definition of the rexgex