Separate Hands?

Generally, I study everything hands separately and advise my students to do the same. I start with the left hand, which for me (as for many) is "naturally" less agile and furthermore one tends (especially if inexperienced) to listen to it less than the right.

I know that other pianists have a different habit; they prefer to play hands together immediately. I find this method better even for strictly musical reasons: for example, precisely in Sonata K 545, even the Andante can be appropriately studied hands separately! It is useful to study the left hand alone to properly study the sixteenth-note groups (the classic "Alberti bass"), taking care of the sound and phrasing (yes, because even the "Alberti bass" can have its own phrasing). And then naturally the singing of the right hand: tone, dynamics, phrasing.

I completely agree with Maestro Sfredda; studying hands separately is fundamental to properly understanding the phrasing of the right hand and the left hand, which is at least as important as the right.

I also agree on studying with hands separate. Perhaps not for long. Trying to join the hands by seeking coordination of gestures, then returning to studying with hands separate as a way to deepen knowledge of the piece. Alternating with studying with both hands together (even for small fragments or small phrases) will be useful to clarify to the pianist which parts they still need to study with hands separate and which they do not.

I agree that studying the left hand is fundamental. Even in memory training, "left hand from memory" and "hands separate from memory" will be extremely useful!