The Boost library brings useful features to C++ that are not yet in STL. For example, the C++17 filesystem library was in Boost for several years. Until the most recent compiler releases, C++17 filesystem required Boost.
Boost install requires several hundred megabytes in general.
While MacOS and Linux users can simply install Boost via commands like
brew install boost, on Windows installing Boost from the
Boost binary distribution
takes a lengthy build procedure.
pacman -S mingw-w64-x86_64-boost