I use use the right shifter almost exclusively. However the one or two times during every ride I want to get immediately to the big or small ring with out going through the cogs on the rear just makes it hard to want to have the paddles on the left shifter do anything else.
With the buttons underneath the top of the hoods that you can assign to control your Garmin or other device if you have D-fly for your 11 speed or less Di2, I haven't even seen a need for any other things to re-assign the left shifter to.