Small faces are faces where: the length of all edges is less than the specified length and the surface area of the face is less than the square of the specified length of an edge
To check for small faces, select the Negligible Geometry and Small Faces check boxes and specify the maximum edge length in the Length of All Edges check box. Faces with all edges less than the specified length are small faces.
In fact it doesn't suit me.
With this function we enter an X value and we find all the faces with no side > X and whose surface area is less than X². I have a problem with the first side length setpoint. For example, if I'm looking for surfaces of less than 400mm², I type 20 in the length box. but I won't find the 25 x 15mm rectangles that interest me anyway because 25mm > 20mm