Someone might have data on this, but in easy terms I'd just assume this:
You want to use guys that are fighting for positions. Risking production from a player on a team that has their seeding clinched is not favorable since they may only see half of their normal carries/catches or less. Sure, they could still go off even with limited touches, but their chances of doing so are less.
As far as guys on teams who are fighting for spots - I'd say their chances of doing well/poor are the same as any other week...it depends on who they are playing. Now, if they are playing a team that's already clinched, they may get a bigger bump up providing the team rests its major players on defense.
Nothing earth shattering here, I'm sure...just making assumptions based on fantasy football logic. Play players who have good matchups, and if you want a maximum chance to score, use the guys on teams fighting for spots or teams that are already out of the playoffs that are playing for pride.