This may or may not be what you want, depending on the use case. If you change an important variable in the Makefile (e.g. CFLAGS), you might want to recompile everything. However, if you're just adding a new source file to the Makefile, you definitely do not want to rebuild everything.

I prefer to run `make clean` manually when necessary rather than adding a rule to rebuild everything "just in case". But I can imagine that this might be useful in some cases.

I like to put CFLAGS/CXXFLAGS et al in separate files that just define the corresponding macro. These get included in the makefile which has dependencies added to rules that reference such a macro on the file that defines the macro. E.g. the .o rule for C++ has a dependency on the CXXFLAGS which defines CXXFLAGS. Change CXXFLAGS and things rebuild, mess with LDFLAGS and you re-link etc... Handy if you need it but you can end up with lots of little files.