There will almost certainly be rookies or second-year guys who are clear future assets who you can't realistically start this year yet you may want to keep on your squad. Same for injured players.

There will probably be a couple of win-now pieces on every team, and teams should have the freedom to add/drop to adjust those pieces to their heart's desire imo. I don't really see how limiting the number of add/drops would encourage owners to stay active.