After the recessional (when the wedding party leave the ceremony), photographs will be taken outside the ceremony venue. Everyone then makes their way to the reception. The ease and timing of this depends upon the location of the reception.
If the reception is in a separate venue, the ushers should now come into their own, organising both guests and transport.
Once the bride, groom and wedding party have left, the ushers can tactfully direct any guests towards their cars or onto transport heading for the reception.
Either the best man or chief bridesmaid should phone the caterers to let them know that the guests are on their way.
A couple of ushers must stay behind and clear up the venue - gathering order of service sheets, checking for belongings left behind - before heading to the reception. They can also collect flower arrangements for the reception, as appropriate.