I was asked to shoot my nephews wedding and of course I was pleased as it meant that he and his fiancé were pleased with other photos that I had shot of them...my first wedding...yikes. It was cold and windy and rainy so outside shots which are my preference were out of the question. My speedlight is a simple SB600 and in a small room will do well but in a big, dark church or hall...I knew that it wouldn't do it but I endured. Make sure that you can visit the venue ahead of time, ask ambient light adjustments that can be made to suit you. High ceilings can be an issue, hope for a lower ceiling to aim your light towards the ceiling or at an angle of 45 degrees. Shadows cast will be the biggest issues. One very good advice that I read was to aim your flash behind you to a wall that will bounce all your light...it actually works but you have to be careful that you don't blind anyone standing behind you. If you can afford a better speedlight, ask in the store which one is good for that type of shot. Good luck!