It depends on the primary branch and detail branch. Spending time in Infantry, Armor, Field Artillery is probably worthwhile for those assigned to some primary branches, but I don't see the benefit of detailing Chemical.So considering an Army Career, would it be fair to say branch detailing is not the best move?
MI, AG, FI, etc are pure staff functions. I am by no means an expert in these branches, so I will defer to those who actually served in them, but my perception is that what knowledge is lost by detailing is not as great as in more technical branches.
Signal Corps and Engineers have technical components that are greatly enhanced by their respective BOLC's and first tour experience. As a former EN officer, I would not have wanted to detail my first tour rather than lead an EN platoon.