Royal Licences issued to ancestors
The commonest use of Royal Licences was to give cast iron proof that a beneficiary had complied with a will clause that gave them an estate on condition that they changed their surname and arms to those of the writer of the will.
In two of these, Brown and Busfeild, that is exactly what happened. But for the other two, Powys which changed the name and Powys-Lybbe which changed the arms, the reasons were far more complex and are investigated in the "Name changes" page that is linked at the top here.
Here they are: