org-indent-mode is an interactive autoloaded Lisp function in `org-indent.el'.

(org-indent-mode &optional ARG)

When active, indent text according to outline structure.

Internally this works by adding `line-prefix' and `wrap-prefix'
properties, after each buffer modification, on the modified zone.

The process is synchronous. Though, initial indentation of
buffer, which can take a few seconds on large buffers, is done
during idle time.