how effective is this feature especially BPM wise?

They might as well make it mandatory.

BPM's
Waveforms
Accurate Loops
Accurate FX
Broken files

the list is long on why you should build your overviews.

Building overviews isn't really an option.
As Prinvale' said, we should make this mandatory.

The auto bpm is very accurate. The best one I've ever used.
Just make sure to set the range according to what type of files your wanting to add bpm info to.

Add autogain to Prinvale`'s list.

As far as the BPM detection, I would agree with Zach's comment that it's the best thing out there for that. In my experience it's about 99.5 percent accurate, giving good results even on older music with a lot of tempo variations (seems to do a good job of finding an average).

The one ongoing problem I run into is certain types of "shuffle"/"triplet" rhythms sometimes return a result that is about 1/3 less than the real tempo. Depeche Mode "Personal Jesus", for example, gets calculated at 98 instead of the 130BPM that the song actually is.

My workaround for those songs is to select the (incorrect) value in SSL (all digits), copy, then paste into the calculator, multiply by 1.33333333, then paste the result back into the BPM field for the song.

for less button presses on your calculator multiply by 4 and divide by 3 ;)