I know it is recommended to listen to mixes in mono, especially with heavy stereo processing. I have created "fun" sounding effects that disappeared in mono, so I totally understand the concept.
 I'm curious how valid of a concern this remains. I know most phones and televisions these days have stereo output. So is the mono test only to protect the quality a mono listener will experience? Or is it deeper than that? I am thinking of kitchens I've worked in with one speaker in the kitchen and one in the dining room the Beatles come on and the customers can here singing and the employees are hearing the guitar, but I don't know if this is related to the recommendation to listen in mono.
 Any opinions will be appreciated, thanks.

Some will tell you that mono compatibility is no longer relevant in a world where most music is listened to on earbuds. They are wrong.
 
Varying degrees of monophonism (I just made that word up) always exist whenever stereo material is played over speakers and the two sides are mixed in the air. On your TV, in your car, over a club PA, in an elevator, a portable radio at the beach - any time you're not sitting in the sweet spot of an equilateral triangle with your speakers.

bitflipper
Some will tell you that mono compatibility is no longer relevant in a world where most music is listened to on earbuds. They are wrong.
 
Varying degrees of monophonism (I just made that word up) always exist whenever stereo material is played over speakers and the two sides are mixed in the air. On your TV, in your car, over a club PA, in an elevator, a portable radio at the beach - any time you're not sitting in the sweet spot of an equilateral triangle with your speakers.

interesting take, I am going to play a song with a part that I know disappears in mono, and move all around the studio while it plays in normal stereo and see if it disappears anywhere (or anything else noteworthy)

bitflipper
Some will tell you that mono compatibility is no longer relevant in a world where most music is listened to on earbuds. They are wrong.
 
Varying degrees of monophonism (I just made that word up) always exist whenever stereo material is played over speakers and the two sides are mixed in the air. On your TV, in your car, over a club PA, in an elevator, a portable radio at the beach - any time you're not sitting in the sweet spot of an equilateral triangle with your speakers.

Couldn't have said it any better. For evidence, play back music from an iPad.

Who is your audience?  To me that is the question.  
 
For my own music I'm not concerned with catering my musical ideas to someone listening on a phone with less than zero bass response and generally zero stereo field and low quality (as an example).
 
If I'm working with a client that is producing music for a store environment or similar, then it is a different question and mono is suddenly relevant.  

I always understood the purpose of the "mono-test" (sounds like something your doctor would do) was to reveal any frequency problems in a mix.  If you go to mono and the voice disappears behind the guitar then you know you have a problem, so work to fix it.  I was always told "if it sounds good in mono it'll sound great in stereo".

All,
 
What is your preferred method for checking a mix in mono?  I know there are plenty of ways, but I was just interested in workflow...
 
Salud!

bitflipper... a portable radio at the beach ...

kids playing music out of mobile phone speakers (ffs!)

It is a MUST to check in mono, your stereo mixes will thank you as well! I use the mono button in my Focusrite control panel as it's easy to switch quickly. Before my focusrite had the mono button I used the Interleave button in the master channel. Mono is the best way to tell how your mono-ish stuff and your stereo-ish stuff is getting along together. I find I tend to slightly adjust bass and vocals when I switch to mono. Stereo can be deceiving. Good thread!

Blogospherianman
It is a MUST to check in mono, your stereo mixes will thank you as well! I find I tend to slightly adjust bass and vocals when I switch to mono. Stereo can be deceiving. Good thread!

Very true!
 
I use a piece of software to switch back and forth.