First of all, thanks for all the reply.
Just a few more questions:
Can a ppp justify the use of una corda?
I attend some masterclasses, and shock to find out that the students (mostly from local conservertoir), use a lot of damper and una corda pedal, even pieces from Bach, Hadyn! Not to mention romantic peices (even more). But neither the presenters/teachers say anything against them. One use a lot of damper plus una corda pedal in a Hadyn sonata, and I have to admit that he produced some of the most beautiful sound I had heard in that session.
Can I say, using una corda is to create different mood, feel, touch, and color (By the way, what exactly is the mood, feel, touch, and color that justify the use of una corda?). By using Una Corda, I am thinking that the sound may be produced from a different dimension/angle, rather from the same piano. Is it right to think so?
I am doing Mozart Sonata in a minor. Wonder is it justify to use una corda in certain sections, like measure 62-65 in 1st movement, and some in 2nd movement?
Will students be penalised if they use it during the exam? Even as low as grade 3?
Thanks, will really appreciate your answer.