For a good discussion of the couple's match, read this thread:
Couple's Match Algorithm Help for ROL | Student Doctor Network Make sure you read to the end, some of the initial posts in the thread are incorrect.
As already mentioned, using the couple's match if done correctly cannot hurt you. If you list all combinations, you cannot do any worse than you would have done individually. If someone does not match, they would not have matched had they applied individually nor would changing the order of their rank list changed the outcome.
The only reason not to use the couple's match is if you don't have enough ranks. The maximum ROL is 300 ranks, if you each have about 16+ ranks you'll run into this hard limit. In that case, you'll need to decide on a compromise couple's match list, or apply separately.
You can choose to couple or de-couple any time up until ROL deadline, so you can choose anytime you want.
At the beginning of the season, the only question you need to consider is whether you're going to put the couple match interest on your ERAS applications. There's no simple answer to the "right" option:
- Programs in large urban areas with lots of local programs probably won't care. They will assume that your partner will get interviews somewhere.
- Programs that are isolated (i.e. they are the "only show in town") may coordinate between the programs. It makes less sense to offer only one of you an interview. It's possible that if one of you has a weaker application and is rejected from their program, the other will simply decline to interview. It's also possible that one program may be very interested in one of you and convince the other program to invite. So it can work both ways.
You can put your couple status in your ERAS app. You can keep it completely private and still couple match in NRMP -- we would never know. You could also leave it out of your ERAS app, and then if one of you gets an invite and the other does not, you could reach out with the "my partner got an invite and I was hoping for one also" email. There's no right/best answer, just pick what you're most comfortable with