I dunno, would we have been significantly worse had we kept Prince instead of Jerebko?
If we had cut Bass (or gave him away for nothing), it would just have been some combination of Zeller/KO/Crowder/Jerebko (or Prince) getting more playing time, which wouldn't have moved the needle that much.
We would have been significantly worse if we had waived Prince and Bass at the deadline instead of trading or keeping them.
Bass and Jerebko were both very significant parts of the playoff push. If you replaced their minutes with KO, Turner, or Crowder, I think the team would have been significantly worse, particularly defensively. That likely would have been enough for the Celts to lose a few of the exceedingly close games they won toward the end of the season.
Anyway, it's all conjecture, but it stands out to me because unlike the Isaiah Thomas move, trading Prince for pieces instead of waiving him and keeping Bass seemed to have no significant benefit aside from keeping the team in the playoff hunt.
It consolidated two smaller trade exceptions into one larger one. Which didn't end up mattering much, but it existed as a tool if needed, and flexibility has been a driving force of this rebuild. Could Ainge have then released Jerebko and Datome? Sure. But they were there, so might as well get a look at players you've found interesting in the past. Also, releasing players costs you Bird rights of players over the summer, which again reduces your overall options.
Furthermore, it creates an expectation that you'll release a player in a future year, lowering the value of future players on the trade market. This is also true from a financial aspect -- Prince's agent thought he could hold out on giving up money in a buyout until after the trade deadline, and then his client would get both more money (rest of year contract plus what he was owed by Celtics minus a little bit) and team choice. Instead he was traded to a team he didn't want to go to that missed the playoffs.
All of these are small reasons, to be sure, but they are all legitimate, and collectively have benefit beyond on-court results.