align vs equation

Question

I always use align in my documents, and avoid equation. Is there anything wrong with that? My reasoning behind this: align > equation, so why not use it?

Answer 1

While not exactly a bad idea in principle, unfortunately it is a bad idea in practise because align doesn't have the same feature as equation whereby less vertical space is added if a small equation is displayed after a paragraph that ended early on the line. For example, consider

\documentclass[twocolumn]{article}
\usepackage{amsmath}
\begin{document}
hello
\[
a+b=c
\]

hello
\begin{align}
a+b&=c
\end{align}
\end{document}

You should easily be able to see the extra space after the second ‘hello’.

Answer 2

Will all due respect to Will Robertson, actually I think that it is a bad idea in principle, because they mean different things and markup (be it *TeX, HTML,...) should be logical as much as possible.

If you are typesetting an equation, then use equation and if you desire alignment you can use aligned blocks inside the equation.

You can decide easily whether you are typesetting an equation or not, by thinking how to want to reference it. If you only want one equation number to be displayed and see yourself suppressing by hand any additional equation numbers, (say by using \notag) then you are typesetting an equation and your markup should reflect that.