As was told to me by my seniors, MC is for 2 reasons
1. Durability and
2. Better contrast / colors
I've seen some cheap filters wear out after a few cleanings but my cheap single coat Kenko has lasted several years w/o losing any of the color.
While I've not the chance to compare side by side 2 filters of different coating, I've seen enough photos with and without the single coat on. The difference in contrast and blooming is noticeable.
MC isn't too expensive, a decent filter goes for around $30 to $40.