I used to only use my right hand (I'm right handed) or barely use my left hand. AT some point I noticed a slight curve to the left in my erection, so I started primarily using my left hand, and continued to do so until I straightened out.
I have the luxury (as many men on LPSG do) of using both hands at the same time, but I usually only do that as a way to finish myself off and cum. It just feels too good the have my entire shaft being stimulated.