Unlike a chisel, the back of the plane iron doesn’t act as a registration face.
If it isn't flat enough to 'resister' against the chip breaker, you will know it.

If it has flatness issues at the edge it will have trouble with taking a light shaving.

Many of my old blades were not flat at the edges and had to be flattened in order to take a full width shaving. This led me to post on using a light back bevel at the sides of the blade to camber a plane iron.

Here is a shaving from the blade after a fresh sharpening:

Full Width Shaving.jpg

Here is a shaving from the same blade after a few rubs of the back corners of the blade on a hard Arkansas stone:

%22Cambered%22 Blade Shaving.jpg

It only takes three or fours strokes to get change the edge profile enough to change the nature of a thin shaving.

jtk