There are different fantasy games. The league I'm in is an APBA league, the cards-based game where a season of baseball is played with dice and cards which replicate players' performance from the previous year. It's a keeper league, so part of the fun is watching players accumulate stats for next year. I'm pleased as punch, for example, that TJ Friedl may be my starting CF next year.
But card grades don't care about team-based measures like runs and RBIs; they're based instead on individual measures including, critically, fielding grades. So, frustratingly, Trea Turner's season is tarnished for APBA purposes with every error he makes. In the more common Rotisserrie (spelling?) stats-accumulation game, I don't believe that player fielding counts for anything other than how it affects playing time and position.