If you look at geographic categories on Wikitree, it is standard practice to use two descriptors, [town], [county/state etc relevant for the place]. This is because place names are frequently used multiple times over in different countries and we need to distinguish between them.
So we have categories (for example) "Sheffield, Massachusetts", "Sheffield, Alabama", "Sheffield, West Riding of Yorkshire, Yorkshire" and "Sheffield, Tasmania". There are probably more.
This practice is seen across the board. Using the additional descriptors of "Surrey" and "London" distinguishes the location from those places in other parts of the world that have the same name. If we just use "Clapham" we are not following the practice used for place names in Wikitree and could cause confusion for people putting profiles in the wrong place.
When it comes to London, there are different views about whether Clapham (for example) is located in Surrey or London. Both are correct depending on the time period. Some people feel very passionately about this so, in the end, we decided the pragmatic solution was to keep both. "Clapham, Surrey" would be linked to both "Surrey" and to "Clapham, London" enabling all the links relating to "Clapham" to be congregated in one place.