For my part I can honesty say the one thing that causes me the most problem is the bridal party being late. Someone is running late, or someone has to leave the premise to go purchase something missing is just a tic -toc away. The more tic-tocs away we have the more pressure it puts on me when I'm recording your memories for eternity. When all the planning has been completed and it's showtime, everything has to be on time. Your wedding is sorta a show. Your family and friends have responded from all over to watch you guys take that walk down the aisle, light a candle and walk outta there with precision and on time. They get restless easy.
And the majority of the time related to being late or getting started late is usually on the girls. It happens more often than anyone can imagine.
But what it does to me is this. Obviously I have a mental plan in place of how I am going to approach the photography. Such as when I take a certain shot and then on to another shot and now back to where I once was to take another one, the timing has to be in place. However you had practiced the timing is how it should go. Just because one may be running late does not dictake that the ceremony needs to be rushed.
The important thing here is this. The wedding has to be on time and run on time if your photographer is allowed to create awesome photography with you. It takes time to get all the photographs you want. When the timing is late even by just minutes the tic-tocs are gone.
Then because you are late getting to the reception people literally leave as you arrive. Then during the reception the photographer will need you to go with them for a few minutes. Yes 5 minutes always = 15 minutes. But some shots missed earlier need to be made up. Sometimes they are and other times they do not get made up.
And now the last word, the flat bottom line. Is a Wedding Coordinator (long for WC) a worthwhile expense? You'd better believe it is. Not only are they working behind the scenes to keep things moving along, they are making sure each vendor is ready to do their thing when its time. They take so much of the pressure off of the bride and when the bride is not being a concerned with being the self coordinator, flower delivery, cake leaning, bouquet is where still!, oh in the car, I don't have the keys, who has the keys! she can concetrate of getting ready. And of course the WC will keep you on time.
The wedding coordinator and I usually confer with one another so that I am aware of the specific tasks being performed during the wedding and reception and how much time each task takes and to allow me the time I need for creative photography. Remember, no time = no pictures because it does takes time. Not a lot, but just my allotted time...
I highly highly encourage you to look into hiring a wedding planner/coordinator.
Here is a list of a few in case you dont know one right off hand.
Here's several more mentioned on The Knot