I get this particular question many, many times! My venue provides a site coordinator, why get a wedding planner? What's the difference between a site coordinator and a wedding planner? Is there a difference?
YES THERE IS!!
A site coordinator handles just one piece of the puzzle: the Venue. Their "allegiance" is solely to that venue. Think about this, who do they work for? They have been hired by the venue to ensure that the what they are supposed to provide is completed. They make sure that the room has enough tables & chairs, the staff is aware of the nights events and that the kitchen is running on time etc.
A wedding planner will put all the pieces of the puzzle together. Even just a "day of" coordinator provides so much more.Your wedding planner works for you and their sole "allegiance" is to YOU. You hired this particular person to handle the details of the day. They work for you. They make sure that your vision of the day is executed flawlessly. They will be the contact of all your vendors including the venue.
Don't get me wrong there are site coordinators that go above and beyond. They are asset to you as well as the wedding planners. They know the venue, inside and out. So they would be able to tell you the best way to run your ceremony and reception layout. But, what they can and cannot do is limited. Most of the times, they've only met with you once or twice. Aside from emails and phone calls you barely know this person. A planner is the one who gets to know you and your family so they can provide that personal touch. The person during the planning process you can call and vent to without any judgement. The person who will help with the planning woes. Because in the end it can be stressful. There is so much along the way during the planning process that can cause you do be nervous, the planner is that person that will give you that encouragement. Help ease those nerves.

Wedding planners make sure to contact each of the vendors prior to the wedding to go over specific details. If there are any concerns that we or the vendors have, it gets resolved before the wedding day. The site coordinator usually will not have contact with the vendors before the day of the wedding. Unless, of course, the vendors themselves contact them. Which means you are the "middle-man". You refer questions or concerns from one to the other.
A wedding planner is there to assist you with anything that you may have concerns about. Whether it's before or on the wedding day. They offer your a personal touch, making sure that you on your day are stress free. The site coordinator normally doesn't have the time to give you that personal touch, maybe only checking on you 1 or 2 times throughout the event. Again, the main focus is the venue, they have to make sure that the kitchen, the timing and everything else dealing with the venue is executed perfectly.

All in all, both are an asset. When a good site coordinator meets a good wedding planner, fireworks happen. It's the best of both worlds. On your wedding day, instead of having one piece of the puzzle amazing, wouldn't you want someone that knows how to make all the pieces fit and make your entire day flawless? If you had a choice wouldn't you want someone there on your side, "your right hand gal", to help every step of the way with every aspect and not just the venue? In the end it's your day. And don't you want the best people helping you make that day as amazing as you have envisioned your entire life?