If you have ads that you want people to click, then serving a partial feed may mean people click through to continue reading. But a partial feed also means some people will not read.
I have also found that people offering partial feeds and who also have ads sometimes write the partial text in more of a teaser sort of way to try and make me click through. That gets old really fast – even with ad-blocker.
Why don’t you offer what you prefer when reading other sites ?