The Spacing Toggle is a context sensitive indicator that shows whether automatic spacing is:
in the window you are currently typing in.
While typing in a given Client Application window, you can toggle automatic spacing on or off for this window by clicking on the Spacing Toggle or by typing the Ctrl+0 shortcut. Instant Text will then remember your preferred spacing setting for that window and apply it automatically whenever it encounters that window again.
Note that spacing can be toggled
on or off only if it is enabled under the Options Dialog Automatic tab.
Else automatic spacing is always off, and the Spacing Toggle is not even displayed.