While preparing for an upcoming performance of Pierrot, I have been reciting the sprechstimme while practicing my own part. This is probably more entertaining for me than for my husband, trying to work in the next room.
Actually, I frequently sing while practicing, filling in missing voices from the score. Another great exercise is singing one voice in a double stop passage, while playing the other (always fingering both, but just bowing one). Doing so shows one can hear the voices independently, not just as two notes sounding together. I find my students usually can’t sing the bottom voice. As violinists, there is a tendency to listen only to the upper line.
It is crucial to play the entire score in the mind, whether it be a piece of chamber music, a sonata or a concerto. After all, as in most human interactions, it is attention to the entirety that gives real meaning and creates real connections. We probably have all had conversations with someone who is talking at us and not hearing a word anyone else is saying…. not a lot of communication going on there.