The vAPI supports the ability to attach or detach 1) multiple tags to a single entity or 2) a tag to multiple entities at the same time.. but using the New-TagAssignment cmdlet only supports multiple entities if we assume using a pipeline in for the entities is considered parity with the API (it's not, IMHO). Using Remove-TagAssignment does allow for pipeline input, but it's fraught and confusing for a lot of people because you end up having to do a get on existing assignments you want to remove and present those assignments to the cmdlet.
I'd love to have the ability to have bulk operations conducted where I pass in arrays for both all of the required tags to apply and the list of entities to apply them on.. and the cmdlet smartly determines which method to uses... rather than me having to remember that I have to loop through my tag list as a for each and pass the list of entities in from a pipeline from within there... especially if I didn't want to pre-create that variable ahead of time.. It'd be super awesome if I could present in the same value types on creating/attaching tags as I do when removing/detaching them... i.e. a list of objects, list of tags...go perform that bulk operation and let me know if it finished or not.