Good writing keeps one main line and lets the digressions wait their turn. Footnotes and callouts are two ways to hold a secondary thought without breaking the first.
A footnote is for a reference or a small qualification — something a careful reader might want, and everyone else can skip.1 It lives at the end and links back to where you were.
Callouts are louder, but still quiet. They pull a note out of the flow when it genuinely deserves a frame.
When to use which#
Reach for a footnote when the aside is bibliographic or pedantic.2 Reach for a callout when the aside is a genuine warning or a key caveat the reader must not miss.
And sometimes the right move is a plain note, set apart only enough to breathe:
The throughline is the same one the whole site keeps returning to: say less, on purpose, and make the few things you do say land.