I worked both this past semester and this current semester as the the volunteer co-coordinator for the career fair held by three of the life science colleges at Virgina Tech. Most of the groups I'm in are led with fairly strong leaders. However, the leader of this group seemed to be more focused on approval and being liked then the actual task of setting up and executing the job.
I saw first hand the power style of nonassertive or passive. The group leader was very polite and tried to avoid problems with everybody. It was usually unclear whether she was for or against something until after the whole group had given their input. I never saw the passive approach attempted on a superior so in this situation I can't comment on its possible effectiveness.
Due to the passive approach of the group leader, most planning meetings were missed by over half of the committee. Additionally, on the day of the actual job fair, only about 3/4 of the committee even made an appearance; about three or four of them actually helped the majority of the time. When you have a committee this large, to only have that 2 or 3 people helping you out the whole day for an entire career fair, it became very obvious to me that a leader cannot use the passive power style. It may work for a subordinate to use towards his/her boss, but it can't be the status quo for a leader. Especially since this is a professional environment, there shouldn't even be the need of it for emotional situations. The group leader should stick to the assertive or agressive power styles, depending on the situation, to achieve the best results.