Many years ago the 4″ was a typical auger for perch fishing lakes like Mendota/ Monona. You can zip through 24″ ice effortlessly, reduced weight for the long hike without a power head, and 99% of the perch you caught came through the hole with no problem.
But use in other applications becomes too much of a rick. Most 8″+ gills, crappies, bass, and other fish with larger profiles don’t fit. I have a 5″ lazer that I like, and on a rare occasion will get a fish stuck in the hole.
However, a great application for smaller augers is super shallow panfish bites on sunny days. I still prefer to have a larger hole and leave slush in it to block some of the sun. But I do see a lot of guys still opting for the super small augetr for these bites