The completion of Cold Harbor is hyped up so much throughout this series. Jame Eagan tells Helly AND Helena about it excitedly, Drummond describes it as “Lumon’s greatest day”, and Lumon fired three good workers in favor of three known dissidents because they knew Mark wouldn’t complete Cold Harbor without it.
So when Gemma walks into a room and disassembles a crib, many viewers were either perplexed or in disagreement. How could this be the crowning moment? How could it be so banal?
Theories on the purpose of cold harbor fall into two camps:
It’s testing compliance
ColdHarbour Gemma is different from every innie we’ve seen on the show. In mark’s first moments, he threatened to find and kill Petey. Helly assaulted mark and tried to run away. Even Gemma’s other innies show reservations, like when she’s distressed on the plane or reluctant at the dentist or hateful in the Christmas card room.
CH Gemma is different. She’s given the same onboarding question and standard memory wipe as Mark & Helly, but instead of acting out, she complies instantly with the task she’s given.
Kier sought to tame the four tempers to create maximum efficiency, and in CH Gemma, that’s worked perfectly: she has no objections to any prompting whatsoever. Cold Harbor could be about trying to create the perfect employee.
It’s testing severance bounds
We know Cobel was obsessed with reintegration and putting iMark & Mrs. Casey together. She loots Mark’s house for his wife’s things to prod iMark during the wellness sessions, and watches closely as iMark sculpts a tree in front of Mrs. Casey.
We know at least some of the rooms were personalized to Gemma’s anxieties and dislikes; Allentown forces her to write thank-you cards repeatedly because she hates doing that. In the same way, Cold Harbour is personalized to her greatest pain: losing the baby with Mark.
Cold Harbor could be about pushing the bounds of severance; Dr. Mauer says so himself. There is no emotion bleeding through here; CH Gemma tackles one of the lowest moments of her life completely docile and oblivious.
(As an aside, if this was the intention, mark “passed” this test when Gemma did not. iMark abandons his outie’s wife after his outie experienced the most resplendent joy in years, proving love can’t transcend severance.)
What do you think of Cold Harbor? What was it trying to achieve? Was it the best way to achieve either purpose?

It was the perfect test, testing the limits of being severed.
My questions: Why wasn't Mark turned into an Innie when going into CH? Technology upgrade for Gemma?
Is Gemma the only one being tested? If iMark is working on Gemma, what are the other innies working on?
Could the other refiners just not be working on anything? They might be props for Mark. Lumon knows that hoomans apparently need hooman interaction, their work output suffers when they feel lonely and for now (in this current version of severance) they haven't found a more cost-effective solution to this embarrassment. So maybe the other refiners are given truly meaningless tasks that just imitate what Mark is doing just so that Mark feels comfortable enough in his simulated normal work environment to finish his important work. This icky hooman stuff is all supposed to go away with the next version of severance.
I'm going to say it: the other refiners are working on goats.
Before Mark started working on Gemma, this may have been different. There were probably several earlier iterations of this project that ran simultaneously. Petey, Dylan and Irving used to work on real people. Mark working on Gemma just proved so successful that every other test was abandoned and the other refiners were reluctantly retained, for the reason above.
Or, of course, there's always the possibility of more people like Gemma trapped somewhere.
My theory is that Gemma’s being exposed to “generalized” unpleasantries (dentist, airplane) and “specified” unpleasantries (thank-you cards, the crib). We see Helly working on Siena, and Siena is one of the rooms on Gemma’s testing floor, so we know Gemma’s been in a non-Mark refined room.
If there are other test subjects, maybe it’s useful to have a good collection of “general” worries that they can use on everybody.