Here's Mark Hambourg:
Would anyone perform the Chopin 3rds Etude with zero legato in the lower voice?
'This method is, of course, only for slow practice; The action will disappear in fast tempi'. I suggest you read it for yourself since you have so many questions.
Based on what said in the thread you originally posted this in, it appears that you were seeking to imply a rather different meaning.
Here's Kendall Taylor: 'When playing double-thirds legato it is not possible to join both notes of the thirds smoothly when connecting the finger groups, nor when playing the thumb on two consecutive notes. The illusion of legato must be created by securing the smoothest possible progression between the upper notes of the R.H. when rising and the lower notes ofthe L.H. when falling;...' Principles of Piano Technique ad Interpretation.
I was quite surprised to read the first quote by Mark Hambourg. Lifting each finger of the lower voice before moving on is not the way I was taught to play legato. The exercise itself, though, is a very useful one for listening to and perfecting the legato of the top voice.
And that I would say is the point. Yes, it's only an exercise but one well worth considering - more about the ears than the fingers.