Need? Probably not. Want? Maybe. Couples have been throwing weddings for centuries without the help of the clipboard-carrying, headset-wearing consultant. These planners can be extraneous for couples who have the resources to pull together their own events, and the consultants' services can be expensive. Wedding planners are amazingly helpful in some situations, and their services range from helping you with an overall game plan to full oversight through the wedding.
If your budget permits, you can hire a consultant who will take over in finding vendors, finding a venue, negotiating contracts and more. If full-service is too great an expense, find a consultant who can get you started with checklists and vendor recommendations. Another option is to hire a wedding planner for the wedding weekend to push the bride down the aisle, make sure her dress is hung up in the hotel room and set up the hotel's sound system when the DJ's goes out.
Get recommendations and meet with planners to price their services. Some are hourly, while others charge a flat rate. Make sure he or she makes you feel comfortable. It's going to be a stressful time, and part of the planner's job is to take away some of that stress.