This command enables access for assistive decives on Apple OS X machines via the command line, or via Apple Remote Desktop. This is needed for software like SpectacleApp or Sizeup. Mavericks In Mavericks Apple changed the permissions so that every app has to be given permission individually.
Therefore we need to do a bit more work.
In the lower left corner of the Accessibility window, place a check in the Enable access for assistive devices box and close the window. Return to the Adobe Connect meeting room and click the Share My Screen button. Selecting Applications or Windows as a screen sharing option should now allow the available options to display. OS X Mountain Lion’s method to enable assistive devices. After installing it on Mavericks, SizeUp gave us the familiar message about enabling assistive devices.
Not much info out there that I could find. A reference on an application site raised an eyebrow though. 
It seemingly allows applications to act as keyloggers. Pretty obscure way to hide a security feature, and makes you wonder why the software would need it, although in TextExpander's case it seems fairly benevolent.
Is TextExpander a keylogger? Is TextExpander a safety risk? Are you spying on me? While TextExpander does indeed log keystrokes, these keystrokes are never saved or sent anywhere. Moreover, TextExpander empties its cache whenever you type the spacebar. Thus, TextExpander hardly ever remembers more than 20 characters of what you most recently typed. Using TextExpander does not compromise your privacy.
Why does TextExpander force me to enable access for assistive devices? For privacy reasons (see above), Mac OS X does not allow third-party applications (such as TextExpander) to log keystrokes, unless access for assistive devices is turned on.