One of the reasons, but not the only one, is what they see on the monitor is off in color and brightness. One of the ones I normally hear from people is that their prints came out quite dark or an off color and they want to immediately blame the print lab. Why Do you need color calibration? If you are editing your photos and doing anything beyond hitting an automatic fix, you are trusting the monitor to be true to life. Using free third party software you can get a better reasonable calibration from both but especially the smile. If you want something a bit less aggressive the Datacolor Spyder4Express is a better option although you’ll need the next model up from Datacolor for multiple monitors if you use their software.
Short Answer:The X-Rite ColorMunki Smile can be a bit aggressive & warm with its calibrations but mostly works for what you need on a budget.
