I like the trade.
Not because I think Holiday is 'cooked', but because I think it's a deal that could work well for both teams.
With Porzingis' health issues and potential for being traded, combined with Horford's age, we really need some quality size/depth up front. Looking at this career numbers it seems Gafford is both foul prone and injury prone, so we probably can't depend on him too much, but he is a quality big who can rebound, score very efficiently and defend and could potentially be a very high impact guy when he's on the court, something like a Rob Williams.
If we can maintain a big rotation of Porzingis, Gafford, Horford and Kornet then I feel like that gives enough quality redundancy in the frontcourt that would allow is to better manage those injury risks of Gafford and Porzingis.
PJ Washington gives us another quality wing with size who can shoot, score, rebound and play multiple positions on the court. This would give us some nice insurance in case there are issues with Tatum's return, and also gives some help for Brown while Tatum is out.
It's also a fairly low risk move, as both guys I believe will be on expiring contracts next year, so if they don't work out for us they would be easy to move.
It might just be the kind of move that can help the Celtics stay competitive this year while Tatum is out, while simultaneously helping giving some options to save money the following season.