With mksite.sh it happens that the list of files to be generated is
not usually defined on the commandline. Instead the sitefile is being
scanned for the target filelist - those lines starting with
<br><a href=filename specify the filenames that
the mksite.sh script shall take care of.
--filelist is the commandline option to get the result of this scan over the sitefile. It prints the filelist being generated - I am using this option sometimes to postprocess a list of generated files during selftest checks of the project: the mksite.sh script and its faster mksite.pl cousin are called with the same options and the resulting files (--filelist!) are checked whether they are identical.
--files is the inverse option allowing to restrict the series of files to be touched during a site generation run. The sitefile will still be scanned (as it can contain static options atlast) but only one file is being regenerated. Caveat, of course, crossfile resolution of information can not be done like this as the other files in the sitefile --filelist are not even scanned for information. Therefore you should better not try to restrict --files to just the sitefile as it usually contains the last "date" and "title" of the --filelist which are not available.
Restricting the list of touched files is an important option for
large websites since the processing with sh/sed is often dramatically
slow. Using the --files option allows to have a quick preview of the
generated result of that one page being currently in the making. Sure
you should issue a full regeneration of the website when you are done
with editing that one page. In fact this mode is so important that it
is not required to say "--files= a b c"
but instead
just run
sh mksite.sh site.htm a.html b.html
Note that the sitefile is given by its source filename while the generated files are given by their target filenames - in the sitefile the touched files are also given by their target filenames. As an extra it happens that the explicit files do not need to be part of the sitefile filelist. That allows you to burn any sitefile envelope around any html body text.