I do it quite often here and I think of them as footnotes to my writing, because they are tangential thoughts, but still important to what I’m trying to express that it shouldn’t be considered a bonus: the asides are more like a public “note to self”.
It also makes the writing feel more raw and stream of conscience-y. (I don’t have a better word to describe it.)
For work email, I suggest writing it as simply and direct as possible while still being polite. People really don’t like reading essays for work emails.