After the recessional, you need to have music to entertain the guests while moving them out of their seats. After you file into your limousine or begin taking pictures, the guests will usually hang back a little bit and chat before they make their way to their vehicles for the reception. It is appropriate to have scheduled about 10 minutes of music (if you have a large guest list) so that even the last to file out do not have to do so in silence and that those who hang back a little can still feel excited about the moment.
This music should make a smooth transition from the recessional music so they flow into each other rather than having a sudden, abrupt change. This often easy to accomplish because you want the postlude music to also be lively and spirited so the guests can start getting excited about the reception and party. When your guests are excited and uplifted they will look forward to the dancing and partying to come after the ceremony as you celebrate your union.