0.3mm shims for trailing axle

In the Haynes and Skoda workshop manual it mentions adding 0.3mm shims to the rear wheel bearing to eliminate axial play. Now I have done work many times to this area - new outer seal, o ring, cylinders and new drums, but have never considered adding shims. I just reassembled. So is this something I should be looking at? How is it possible to determine if they are required and how many? Up to 3 are allowed!

Thanks for any input.