I'm still reserving judgement on all of this, and I think that we will hear quite a bit from the opposing camp tomorrow. Magness, the Gouchers, Epstein, will all have to respond to Salazar's statement. I wouldn't be surprised if like Salazar, they begin to air out dirty laundry in the form of personal communications (texts, personal emails, documented conversations with teammates, etc.). If so, this will all get even uglier than it already is.
That being said, I think that Fleshman's interview laid out very clearly what the benefit of thyroid medication can be to an endurance athlete. She explains that a healthy athlete can push themselves hard enough through the use of altitude tents/altitude housing, and overtraining that they damage their thyroid. At that point, the medication can help their thyroid function normally and the athlete to push themselves harder than they would be able to without it.
http://www.propublica.org/article/elite-runner-had-qualms-alberto-salazar-asthma-drug-performance
"So I talked to my coach, Vin Lananna: I think my thyroid is suppressed. He said that could very well be it, you're not responding to the training anymore, you're tired all the time. And I was like people go to this doctor, Alberto knows about him and I'm thinking about reaching out. And this was the most embarrassing moment, but the really important turnaround for me: my coach looked at me and he goes: "Ya know, you could do that, and if you want to do that, it's your career, and I don't think there's necessarily anything illegal about it, but the reason why your thyroid is as messed up as it is because you're not resting enough, you're sleeping in an altitude tent, and you're training too hard. And you have to back off, you have to change those things, you have to take responsibility." And that made me so embarrassed that I was thinking the other way."