Cesar, I'm trying to understand where you are coming from and I don't get it.
Yeah, Semi was "irrelevant" in the sense that he was a fungible player. Most second rounders are irrelevant in that way.
Paul Reed is irrelevant.
Jericho Simms is irrelevant.
But a team has to cover almost 20,000 minutes in an NBA regular season with a 15-man roster and a $136 million salary cap. Semi is on the Bucks now (not in Europe, not on the street), because he can soak up some minutes with okay NBA-level play. Milwaukee thinks Semi is worth $1.7 million this year. Sure, the Celts could have cut Semi and signed someone else to do Semi things, but Semi was on a second round contract (four years, $6.05 million, partially guaranteed) so Semi's theoretical replacement would need to fill 15 minutes per game with replacement-level 3-and-d...for under $1.5 million per year.
I mean, 15 minutes per game of 3-and-d....
Ryan Arcidiacono will give you that--for $3 million per season.
Ty Jerome will charge you $2.4 million per year.
An NBA team that can get advantageous production relative to cost from those back end roster spots can pick up an extra win here or there. Maybe that leads to making the playoffs, or a higher seed. Maybe it is irrelevant. For all the talk of the Celtics getting a "third star," there is no way to accumulate difference-makers at the top of the roster unless the team creates some value by covering those thousands of non-star minutes as cheaply as possible. He wasn't a huge win, but he was a good pick.
I can't believe I constructed a whole post about the value of Semi Ojeleye. I cursed him so many, many times.