Honestly, I fine it hard to believe they are playing Holt mostly to see if he is a keeper. Not in a pennant race in the middle of August and not against the Yankees--whom we lead by 4.5 for the AL East--or the Guardians, whom we lead by 2.5 for the second best record in the AL. For now Holt serves a useful purpose because of his versatility, especially when Farrell is carrying 13 pitchers and has infielders who are out (Pedroia) or hurting. I agree he is master of none of the positions he plays and that his hitting this year is very subpar.
Nevertheless I disagree that he is a liability when he is on the field. Here's why. Since he resumed playing on July 16, he has played in 29 games during which the Sox were 18-11, a winning percentage of .620 vs. the .576 the Sox have for the season to date. I also looked at his game log for those 29 games and specifically at the losses by 1 or 2 runs when one can presume a single hitter could have made a real difference. There have been six games the Sox lost by 1 or 2 runs in which Holt played. Of those six, he actually contributed to the offense with one or more hits or rbi's, or he had 0 at bats and was probably a pinch runner or defender. The single game when it is fair to say Holt had an adverse effect on the outcome was Monday's 5-4 loss in which he was 0 for 4 and committed that error (which I also think was a tough play). I did not charge him with the 4-3 loss to the Yankees when he was a pinch runner and was caught stealing on a 2-0 count with JBJ at the plate because I believe Farrell had called for a hit and run--2-0 count is ideal for that--that JBJ missed. Plus it was a close play even though Holt is not that good a base stealer.
I agree completely with what you said about our not knowing what is being decided behind closed doors and that all we can offer is our opinion, and I certainly respect yours. But I also disagree for the reasons stated above. DFA might be a consideration, but in August in a pennant race there has to be a better reason for playing Holt. Interestingly, he only missed one game in the 16 games he was active for in July. In August, he has not played in 5 of 18 games. This is mostly because Devers and Nunez have been added to the roster, both are infielder, and both can hit.