Mixing in stereo has its issues, many fail to check their mixes when translated to mono, or even more extreme scenarios like speakers wired backwards.
PANIPULATOR 2 Free Plug-in
Boz Digital Labs have created the PANIPULATOR 2, it lets you know what your mix sound like summed to mono? Flip a switch to find out. What if someone wires their system so that they can only hear the left channel? Flip a switch to hear what that sounds like. What if they reverse the wiring on one of their speakers? Flip a switch to find out to see how that will affect your song. These are all common scenarios, and the last thing you want to do is find out is that your mom’s voice, that you thought was buried in the mix, pops out when played over the loudspeakers at Nordstrom.
Panipulator will barely make a dent in your CPU usage, so there is no reason that this plug-in should not be a default on every single song you mix.