The concept of "need to know" is often invoked to justify a default behavior of hiding information even from highly trusted allies (you see this very often in fiction; Mistborn contains one and Shadow Children and The Reckoners contain far worse examples).
Applying this policy to people whose allegiance isn't in question is almost always wrong even on purely strategic ground. Any time any mission goes south, it's very likely that someone ends up having to fill a role the commanders didn't foresee. It's ridiculous to expect the long-term conflict in those examples to play out without this ever happening. Do writers think fault tolerance isn't a thing when it comes to people in the field? There's also the increased damage done by something happening to one of the higher-ups.
The only argument given in any of the examples I listed is "what if one of us gets captured". It's paper-thin because that's an extremely remote possibility compared to the odds of someone needing information you didn't foresee, and besides, if they're going to be helping your cause, they already need to know at least who they're getting their orders from, so having any member of your force get captured still leads to a chain reaction that threatens to undo your whole organization.
The reason I care so much is because of the values of truth and agency - a very strong reason for a default behavior of openness, and only keeping secrets when you aren't certain of their allegiance. But even if we believed neither of those have any value, it takes a contrived situation to make it wise to keep info from highly trusted allies.