Here are some realistic things a wedding coordinator will do to give you a better idea: 

-They will meet, greet, and guide your vendors. Your rental company bringing chairs/tables doesn’t know which exact loading dock to go to? Your venue is asking where exactly they should set up the sweetheart table or exactly how many seats they’ll need for the final guest count on the day of your wedding? The florist wants to hand off the boutonniere and make sure it’s in a secure place before the groom arrives at the venue? Your day of coordinator can handle all of these things, instead of you as the bride or groom needing to worry about this hours before you walk down the aisle. 

-They will initiate and facilitate key moments during your wedding. Walking down the aisle? Your day of coordinator will make sure to have your mingling guests seated in the appropriate seats, coordinate with the DJ, quartet, or Spotify playlist for processional music, line everyone in your wedding party up (even if its just the groom, bride and parents!), and cue with music for walking down the aisle. Want to make sure you cut your beautiful cake at a specific time? Your coordinator will bring out your cake knife, make sure your DJ knows to make an announcement, make sure the venue knows to bring out the cake if it isn’t out already, and prepare a plate with two forks for when you cut a slice. 

-Setup? Breakdown? Troubleshoot? Anything specific that needs to be brought out in the middle of your wedding? Making sure your card box/guestbook is secure? Your wedding day of coordinator will be there to manage and handle the details as you guys have discussed beforehand, as well as things that will come up during the actual wedding. And believe me, things definitely will.