-Do not delete debian/files, or files listed in debian/clean. When do you
-want to use this? Anytime you have a debian/rules that has 2 binary targets
-that build different .deb packages; for example, one target is binary-arch,
-and the other is binary-indep, or one target builds the shared library, and
-the other the -dev package. If you didn't use -k in these cases, then
-debian/files would be deleted in the middle, and your changes file will
-only contain the last binary package that was built.