I tried it for the first time yesterday just to see how it works.
Obviously with it being my first/only time trying it, it felt a little cumbersome, but I am willing to bet it gets more fluent if you use it routinely and get the pattern down.
I am used to driving flatbed cranes, bucket trucks, etc. and grew-up using mirrors to park and backup, so of COURSE I view this feature as an unnecessary gimmick... but I totally realize that it very-well may be a VERY commonly used feature by others.
What I noticed in my one-and-only use... It did an amazing job perpendicular parking my Pacifica between two cars in this parking lot... but for better or for worse, it parked me PERFECTLY and EVENLY spaced between the two cars. The problem is, both flanking cars were parked crooked in their spots in the same direction... So now *MY* car was not "straight" in it's spot. Apparently the system favors positioning the car the best it can between objects, and ignores the painted lines.
I have yet to see if it even works at all if there are no cars (just painted lines)... or if there's only one car in one space and the other is empty. No idea. Hoping to test out the parallel parking some time.