As far as I can tell,
a single line align renders identically to an equation.
So on that basis, I have just been using align everywhere,
as it makes it easier later if I decide actually I need to add another line to expand out a formula, to enhance the explanation.
Is there any downside to this?
alignrenders identically to anequation" -- is incorrect. Inter alia, the amount of vertical whitespace above and below single-line displayed equations of typeequationandalignare not the same. – Mico Nov 10 '17 at 03:27