It's the premier porting tool for making cross-compilation harder.
I think the main raison d'etre was automatically linking transitive dependencies for static libraries so that builds on system with or without dynamic libraries could work more or less the same. E.g. if you statically link e.g. Freetype than wether you also need to link zlib, libz2 and a bunch of other stuff depends on how Freetype was built but the .a static library contains no information about those dependencies since it is just an archive of object files with a symbol index. libtool records these dependencies in .la files so you don't have to guess.
It does have many questionable decisions like silently dropping (some) compiler flags it doesn't know about. I wish I never had to deal with it.
I think the main raison d'etre was automatically linking transitive dependencies for static libraries so that builds on system with or without dynamic libraries could work more or less the same. E.g. if you statically link e.g. Freetype than wether you also need to link zlib, libz2 and a bunch of other stuff depends on how Freetype was built but the .a static library contains no information about those dependencies since it is just an archive of object files with a symbol index. libtool records these dependencies in .la files so you don't have to guess.
It does have many questionable decisions like silently dropping (some) compiler flags it doesn't know about. I wish I never had to deal with it.