Blur the Application, in the parameters of texture, equivalent to the use of the same texture, but pre-blurred in Photoshop, for example, using the Gaussian Blur filter 🙂
You are all well know, Blur, it's just a blur, and nothing more. There is no mystery or hidden meaning is not, in fact, as well as any significant effect on the rendering.
The meaning of touch only when you do a bummer separate blurry textures in Photoshop, for which the effect. Then you can do it directly in the 3ds Max, similar to the way in using ColorCorection or the ColorCorrect , it also can adjust the color texture.
The situation can be any in which you personally took to blur some texture. If such situations arise you do not, then you and this option is not needed. Especially coming up with the situation, anyhow use it - should not be😁
For example, I twist Blur when as a Bump texture, I use the Diffuse texture with very sharp detail and higher contrast. Otherwise, without Blur the, material texture may seem very harsh / rough. Furthermore, depending on the lighting conditions of the scene and the reflective properties of the material, artifacts may appear as a white rash. This is especially true when BRDF Ward. But then again, this is only particular cases and the need to look at the situation, applying Blur only where it is really appropriate😉