In one very easy word, YES!
Why do I think everyone should have a wedding planner or at the very least a wedding planner for the day of the wedding? Well, I planned my own wedding. The one thing every bride needs is someone who can look at all the moving pieces of the day without getting caught up in one thing.
As they say...the show must go on!
Also, have you ever heard of those horror stories about the bridesmaids forgetting a dress, a groomsman forgetting rings, an unexpected rain storm, or NO CHAMPAGNE? The horror. Thats where the wedding planner can swoop in and save the day. She (or he) will be at your service from the rehearsal to the end of the reception. And did I mention they will be the only person who is truly unbiased. They will do anything and everything the bride and groom want and make sure all the unwanted mess stays out (trust me, my wedding had some unexpected turns and I didn't have a planner there to rescue me).
Now, I look happy in the photo below (andso does my handsome husband, hes very modest) but I was also directing my photographer the entire time. I am extremely Type A (which makes me a great planner) so this was ok for me. However, most brides don't want to deal with this. So the wedding planner is there to help.
All in all...get a planner!