Probably the most popular is having the Piper lead the Bride up the Ailse at the beginning of the ceremony and leading the newly married couple down the ailse and out of the kirk, followed by playing as the guests leave the kirk. The Piper is usually retained to play at the reception, particularly at the symbolic cutting of the cake. But this is something you can improvise on yourselves but remember you can overdo it!
What music to play? It is best to consult with the Piper before choosing, but most Clans have traditional pipe music associated with them such as 'The Gathering' and 'The March', which you may wish the Piper to play and of course most appropriately for a Wedding 'Flower of Scotland'.