Boost has some subdirectories named 'debug' which contain static files used by some Boost libraries and their dependencies. In some build systems, like MSVC, the 'debug' directory is a directory where intermediate build files, such as object files, are put, and these directories are dynamic in the sense that there contents can always be regenerated from source. A common, if perhaps erroneous, technique of forcing rebuilds in these systems is to wipe out the 'debug' directories. If Boost is in some tree where the 'debug' directories are all being wiped out indiscriminately, then the Boost 'debug' directories get wiped out and source using Boost libraries and/or their dependencies which have 'debug' directories will fail to compile. Yes, I know in the age of IDEs that no one is supposed to build like that anymore, or that it is a very good idea not to put Boost in some tree where the end user decides to arbitrarily wipe out all 'debug' directories in order to force a rebuild, but these things can happen. Because of that this is a gentle suggestion that Boost in the future choose some other name for a subdirectory than 'debug' for those libraries using that name.