difference between `make clean` and `make distclean`

difference between `make clean` and `make distclean`

I installed ffmpeg from sources with help this page.
https://trac.ffmpeg.org/wiki/CentosCompilationGuide
I noticed that most of this tutorial calls make distclean after make
install. But only libvpx calls make clean after installing.
According this document,
http://www.gnu.org/software/automake/manual/automake.html#Clean make clean
deletes all files that make created, and make distclean deltes all files
that ./configure created.
make clean
Erase from the build tree the files built by make all.
make distclean
Additionally erase anything ./configure created.
I understand that make distclean is called for for next installation, but
I could not understand why make clean is called after installation.
The installed ffmpeg works without problem. So I asked this question
because I only want to improve my knowledge about linux. It would be very
helpful that someone give me a explanation for it.