Andrew,

It simplifies drawing circles where the target circle must be internally tangent instead of only externally. Or relevant constructions with Arcs.

It also avoids the repeated sequence:

Step 1: LI
Base point
Target point perpendicular on circle/arc, Auto Snap or forced by SU 
(or center snap SC of if that is easier)
QQ

Step 2: RM
Drawn auxiliary line of first step
Far side of circle/arc
QQ

Step 3: Use the intersection for another task, Auto Snap or forced by SI/SY 

Regards,
CVH