You can get really fat notes in the track view PRV by zooming in vertically, but not in the piano roll. I'd prefer to be able to zoom in further but the application doesn't allow this...yet it does in the PRV...I don't understand why this difference/limitation exists.
I'd prefer to work with fatter notes as it makes tasks which involve vertical positioning of the mouse (e.g. setting per-note velocity) much easier. As well as that, I just prefer to use that level of zoom when working across just one or two octaves, I find it easier on the eyes.