The Boston Red Sox lacked an experienced left-handed reliever in 2019 – only Darwinzon Hernandez and Josh Taylor, albeit both were very good. However, adding a veteran lefty would not hurt the bullpen.
Will Smith would have been a target for the Red Sox as he just had a dominant 2019 season, 152 ERA+ and 13.2 SO/9. He is projected to have a solid 2020 season, 3.57 ERA and 11 SO/9.
He would have definitely solidified the back end of the Red Sox bullpen and could have been their closer.