I will update their position only for their actual ratings (ie. If i draft a guy listed as a SS, but actually a 3b fielding wise, I'll update that), but that's the extent of how often I change. It does not matter for GG or SS as they take the position you actually played throughout the season. The only place I can think it might come in handy is if you're trying to compare stats for different positions. I believe if you sort by positions it will sort by listed position if that makes sense.