Autoconf, Automake, and Libtool were developed separately, to make tackling the problem of software configuration more manageable by partitioning it. But they were designed to be used as a system, and they make more sense when you have documentation for the whole system. This book stands a level above the software packages, giving the expertise of its authors in using this whole system to its fullest. It was written by people who have lived closest to the problems and their solutions in software.
For those times when ./configure says No such file or directory, or in my case, when writing a ./configure-able program for the first time in awhile.