For me, unless there is someone in free agency that you want I'd keep em on the roster to eat up some pre-season game time to keep your starters (that don't need a lot of play familiarity) healthy for the regular season.
Especially O-linemen. If your short on O-linemen in pre-season because of injury you can sometimes get guys playing on the O-line out of position. Like WR's playing center etc.... And that could lead to more injuries. Unless jdb has fixed that. You want to keep that O-line depth chart filled in the pre-season.
Maybe others can share how they approach pre-season.
I always make sure to have 60 guys on my preseason roster. If someone gets injured, then you have a capable backup to start the regular season instead of what's left of free agency. And, as beercloud said, they can be used when you pull the starters in your preseason games.
The only exceptions to this, for me, have been on a few occasions when I have really needed to cut guys during the preseason due to salary cap issues.