Sadly, I think that users haven't seen any benefits - yet.
I can see some potential benefits though: - Some users make a distinction between good-Boost and bad-Boost: they allow the use of some parts of Boost, but not others. I would think these users are helped by a degree of modularity that makes hem confident that by getting good-Boost they are not pulling in bad-Boost. See for instance the Google Style Guide: http://google-styleguide.googlecode.com/svn/trunk/cppguide.html#Boost - Well defined modularity might also make them less suspicious of parts that are currently considered bad-Boost. - As a Boost user you might find it easier to convince your organization to allow the use of specified parts of Boost rather than Boost-whole. - As a non-Boost library developer you might be more happy to tell your users to get specific parts of Boost, rather than Boost-whole.