Fair distinction. There's a kind of unwritten understanding of what programs should and shouldn't do based on isatty, and I've never seen it explicitly documented.

Things many programs do if attached to a TTY: add color, add progress bars and similar uses of erase-and-redisplay, add/modify whitespace characters for readability, refuse to print raw binary, etc.

Things some programs do, which can be problematic: prompt interactively when they're otherwise non-interactive.

Things no program does or should do: change command-line processing, semantic behavior, or similar.