The most infamous deal Boston has made since the Babe Ruth sale to the Yankees was the deal in which the Red Sox acquired Larry Andersen. Of course that is not because Boston picked up Andersen but because of who they gave up when they got him: Jeff Bagwell.
In hindsight of course the trade looks absolutely terrible. Boston gave up a slugging first baseman who is a borderline Hall of Fame candidate in order to get an aging middle reliever who they ultimately only had for 15 games. Boston was in contention in 1990 but was having some difficulties with their bullpen due to injuries to closer Jeff Reardon and ineffectiveness of other pitchers. So they needed to get a good arm in the bullpen. And Andersen fit the bill. He pitched in 15 games with a 1.23 ERA, striking out 25 and walking just three in 22 innings. He picked up a save. Andersen pitched in three games in the postseason, and did lose one of those games. He left as a free agent to the Phillies after the season.
On the other side was Bagwell. At the time, Bagwell was a third baseman in AA ball, but Boston already had Wade Boggs at the position and expected him to be there for a couple more years at least. They also had Scott Cooper ahead of Bagwell on the depth chart for third base. I do not know why Boston did not consider moving him to first base, but they probably should have. Bagwell did not have much power in the minors, but he would certainly not be the only player to develop power at the Majors. It is likely that Boston simply did not know what they had with Bagwell.
Ultimately, this was not a good trade. But that does not mean that it did not make sense at the time.