I found this great article written by Samantha Goldberg, wedding planner extraordinaire.
Read the entire article here.
We all have our own strengths and weaknesses. This is why you really need to know the roles of the various wedding industry leaders.
A wedding planner may be great at managing the wedding process but would rather leave the overall vision in the hands of a floral designer while an event designer may work best with the creative aspects of a wedding but may not have an interest in running the event. The best thing to do is ask your vendors what they specialize in. This will give you much clearer expectations when planning.