one reason for double barrels is good old snobbery. if an aristocratic woman was from a better family or had a 'better' family name part of her dowry could be to bring that name to her new family. examples include the wentworths, the remingtons, and my old dear ancestors the lockharts. another reason could be an indicator of estates owned or regions ruled over. a good example of this is brendas original name saxe-coburg, the names of the two royal duchys the queen is descended from, in what is now germany. many aristocrats have two names, their family name; essex, buckingham, wellington, and their fathers name. remember estates do not always go from father to son. of course the estimable english middle classes cottoned on to this some time ago and many people of the aspirational class have hyphenated their surnames simply to look 'posh'.