In making an application to a Master's program, would I be wise to seek recommendations from academics, practitioners, or both in balance? Or would any credible letter meet the required threshold? Or does this not matter?
I can easily imagine that for PhD programs the balance would be tipped towards letters from academics.
Normally, you should prefer academics, but you want the people who can most honestly attest to your accomplishments and the likelihood of your future success.
However, if the MS is focused on things outside the normal academic tracks, on, say, industrial practice, then a letter from a practitioner who also has the ability to fairly evaluate you would be fine. But for academic subjects or in a field that can lead to a doctorate now or later, academics would probably be better.
But also note that you are appealing to an admissions committee that has a certain background and certain views. You want that appeal to be successful. Thus, if you expect that they all have an industrial focus, then someone (again, who knows your abilities) from that industry would be good.
For doctoral level admissions, you are right. The balance tips more firmly toward academics, but exceptions occur even there.
In making an application to a Master's program, would I be wise to seek recommendations from academics, practitioners, or both in balance? Or would any credible letter meet the required threshold? Or does this not matter?
At the very least, you should have a letter from at least one academic.
Even if you are fifteen years removed from academia, hopefully you can find an old professor and re-connect with them (in that case, I would send them a lengthy e-mail providing some context on the connection you used to have, some of the courses you took, your resume, and a draft statement of interest). I've occasionally connected with professors I had fifteen years ago, and they're usually happy to chat and kind of remember me after having their memory sufficiently jogged.
The rest of your letters could come from practitioners. Some schools will have different letters of reference templates for non-academic letters, but if not, make sure that they focus on academic skills: writing and communication, research ability, and likelihood to complete a graduate program.
We might accept somebody without academic letters, but we would probably put more conditions on the acceptance and/or recommend a probationary status.
(These recommendations are for a humanities program with no real industrial equivalent. Your experience might vary in a more applied field.)
