Originally Posted by Ko.Fe.
From my experience monitor calibration is only necessary half of the in home printing with matching screen colors process.
For regular person bw image posting on internet it is next to irrelevant. Because image is to be ruined by Apple screen on mobile device many NA viewers are using
For this most common scenario I recommend to check your internet shared images from another devices. Like someone else computer. If it looks recognizable, nothing to worry about.
This is also my opinion.
If you are sharing your images via screens (computers, tablets, cellphones, etc) unless every viewer calibrates his/her screen the same way, you have no idea how that picture is going to look on their screen. In this case, calibrating your monitor is pointless.
Physical printing requires a calibrated monitor-printer system.
EDIT (after reading later postings): obviously if you're sharing photos with an important audience on calibrated monitors, you would want to keep your monitor calibrated as well.