It's really down to personal choice and whether there will already be a capable person in your wedding party who would be willing to be the toastmaster.
How Many People Will Be Attending Your Wedding?
If you are planning on having very few guests at your wedding, chance are you will not need the extra hand of a toastmaster. However, if your wedding calls for the maximun number of guests for your venue of choice, a toastmaster may be in your best interest. Not only will they help with any announcements that need to be made, but they will also help with the planning stages and setting up the venue on the wedding day.
If you are planning to make more than just a couple of announcements at your wedding or have multiple speakers attending the ceremony, a toastmaster can help by making all of these announcements for you or introducing anyone about to stand up to the podium. Although announcements are not difficult to make, sometimes it is much easier to have another individual at your side to make sure all of the planned announcements are made and all of the speakers have made it up to the podium.
Needing a Helping Hand
Chances are everyone at your wedding has a specific role and things will tend to get confusing if any extra tasks are added to their list. Although a toastmaster normally just makes announcements and toasts, they are also inclined to help you with tasks such as seating, directing guests and cleaning up at the end of the day. Although you may think you have everything under control in this area of your wedding, it is ideal to have that extra pair of hands in case something is to go wrong such as a guest failing to showup or someone failing to complete their duties at the wedding.