If a team is winning most of its games, it's probably wise not to shake things up and make a major overhaul to its roster.
On the other hand, if a team is mired in mediocrity after several months, the best course of action probably involves making a few moves and giving a team a more competitive roster.
Curiously enough, the Saitama Broncos have chosen not to make any roster moves since the season began in October.