Right now we can have the following situation in a wiki:
a hierarchy like this:
Wiki -> A -> B -> C -> D
with some rights set at the wiki level, then some more "allow" rights added at the level A, some "deny" rights at the level of B, and some more "allow" rights at the level of C.
When administrating the rights on the page D, it is difficult to understand what are the rights that already apply on page D, and where do they come from. This can be useful for the following situations:
- debugging authorization on pages (if a user cannot access a page it's difficult to understand why)
- evaluating the impact of a change in the rights on a parent or on the page D only
- determining the minimmum settings that need to be done on page D to obtain a desired effect, using inheritance.
Note that this is by no means a problem that is specific to the nested spaces, but it becomes more important after the implementation of nested spaces and rights inheritance became more complex and it's increasingly difficult to make the map in ones head or do verification on all levels of the hierarchy for a given page.