Although Pleco breaks the flashcard system into a selection component and a scoring component, in reality, they work together. Spaced Repetition requires a scoring system that's customized for Spaced Repetition, which is what the "automatic" scoring sytem in Pleco is meant to be.There are actually 4 Card selection systems in Pleco, and Repetition-spaced is one of them - it is not a Scoring system.
So one can think of the "automatic" scoring system as the "spaced repetition" scoring system under Pleco.
See this from the Pleco manual:
http://www.pleco.com/ipmanual/flash.html#scoringsettings
Automatic - flashcard scores are automatically managed by Pleco, factoring in your past history with the card (how often you've remembered it correctly/incorrectly) in order to determine how much to increase/decrease the score by after each answer; this is similar to the approach used by other systems like SuperMemo/Mnemosyne/Anki.