Heiko Oberdiek's hobsub package (and hobsub-hyperref and hobsub-generic packages) defined a mechanism for concatenating multiple files into a single file for faster loading. The disadvantage is that it introduces hard dependencies between the source files that are included and complicates distribution and updates. It was principally used with hyperref but is not currently used in any standard packages in TeX Live. The packages are still distributed as simple stubs that reference the included packages via \RequirePackage rather than copying their source.