Yeah displaystyle makes inline equations render like "normal" equation environments like align etc. The difference is obvious with things that take up a lot of

Yeah displaystyle makes inline equations render like "normal" equation environments like align etc. The difference is obvious with things that take up a lot of vertical space like integrals or sums with limits. Sometimes you want an integral inline, but you need to make it \displaystyle. It's annoying to write, hurts readability and badly supported by editors. So d$equation$ makes it trivial to toggle it.