bradley lehmann puts it this way. it's a matter of preference. bradley says some people like strict tempos - everybody steady (organ solo - 'light my fire' by the doors). then, there's general rubato where the beat slows down and speeds up (julie andrews - first part of 'the sound of music' where kostal is conducting a steady beat but they speed up and slow down within the limitations). and finally, melodic rubato - where quantz, mozart, and chopin take the lead. one or more parts 'bend' cleverly ahead or behind the beat.
schumann was a bit old fashioned - so i think it fits, here. also, he was highly sensitive to voice. often, in voice, you have spots where there is an actual 'breath' sort of written into the piano part (and other times you cut short the beat to make the space for the breath) and other times not. when it is not written in - there is a sort of rubato with the melody over a very strict accompaniment. when i hear it the way my teacher plays - it is as if an instrument or voice is singing above the accompaniment and doing whatever it is moved to do. sort of as jazz, today. we hear the inspiration and not just the 'steady beat.'
hope that this is what my teacher might say. i don't really know his reasons. i do know that he has studied with some really great teachers and knows what he is doing. in fact, i kinda doubt what i said before about him sightreading - because he is not known for making mistakes even then. he would at least practice something easy until he 'got it.' apparently this is what he meant to do, imo.