It would make sense to me to use them to effectively bring Withers with you, for the sake of companion reactions/interactions/etc. Not necessary to develop them all to the same depth as the other companions with distinct personalities, but one personality between all of them.
As it is, I'm already consistently torn as to who to leave behind - who is more likely to have story-relevant interactions with whatever comes next - and I just can't justify bringing some hollow companion along at the expense of other companions who might actually be engaging.
(Also...it is a *bit* odd to get the Bard hireling and discover that they only speak with Withers' voice. Hard to imagine Withers trying to sing.)
