When I am asked to play the organ for a wedding, I check for all kinds of specs of the organ on which I will play, such as how old it is, how big it is, whether there are any cracked keys or keys or pedals that may not be working optimally, where the on button is, and more.  

Recently, I encountered an organ with all black keys, and the keys that were usually black were white!  The result was that the keys were very hard to see.  So I had to set up a lantern by the organ to get a better look at them as I played.  This ended up working really well and saw me through the ceremony playing with no problems.  I was glad that I had had just enough time to pick up a lantern to bring with me to the ceremony, even with a wedding ceremony booked with only three days' notice (an all-time record!).

These are just some of the benefits of having me play for your wedding rehearsal whenever possible, as it gives me one last chance to field details like these so that I can play as smoothly and beautifully as possible for your wedding.