Originally Posted by xenologer

It's a MTB thing, nothing to do with velodrome track bikes

The Purpose of a Narrow/Wide chainring
is Not to accommodate two different chain widths

The teeth alternate width, to match with the Inner vs Outer links on one chain
having teeth that touch the sides of plates on All links instead of just the Inner ones, is intended to minimize side-to-side chain motion so it doesn't drop as easily when running a 1x11 mountain bike over bouncy terrain.

it's specific to mountain bikes with single front chainring and rear shifting (1xN drive), has no application for either front shifting, or singlespeed drivetrains.