Yes, calibration matters. If two designers are on the same project unless you mastered the theory in color and reading color mixes whether, in curves, color palettes and profiles being used in a project and for what platform definitely need to match, especially if others on the outside have no calibration.
I have been doing graphics for web and print, offset and silkscreening about 30 yrs and I can tell you, IT MATTERS! Matching calibrations from monitors, inkjet printers "GO EPSON", rip software for films or digital RHODurst printers and UV SK, Offset printers IT MATTERS from the start to finish.
If two systems are way off from each other they will produce entirely differences in white, black, mids and contrast, then yes you have a problem. Use the same brand or specs close to one another. You are working with DMAX, DMINS, Highlights, Shadows, Midtones, and Color Contrast, and Color Hues, so yes it matters. Especially when working from rgb to cmyk conversions or cmyk and rgb conversions. So if you are a designer and are working off a monitor way off of its delta, then how much more to other platforms from the outside? If there is a group that are working on a project, it is imperative that all systems are calibrated. My opinion on the fly!