Does --incremental flag basically do the same thing as jekyll-include-cache for the includes?
Thank you
No. The two features are entirely different.
jekyll-include-cache applies to files that are included into a layout or page or document via the Liquid tag {% include_cached <filename> %}.
--incremental implies that the entire site will build under incremental mode.
Under the incremental mode, the first build will be a full build. Consequent builds will render only those files that have changed since the previous build.