They need to know
You may be wondering just who needs to know what, well, allow us to explain. The secret service needs to know everything that the President is doing during the day and his full schedule in advance for their own security reasons. Their job is to keep him safe at all times after all.
But this can get very annoying because if the leader wants to do anything spontaneous, it is completely out of the question. They need to let these guys know at least four hours in advance and many Presidents have mentioned how annoying this can be. Looks like having security around you isn’t all as great as it sounds.