What is the difference between the scale in model space and paper space?

The scale in the model and paper is 1:1, if the drawing so large then we can reduce the scale. But as per my knowledge scale is doesn't matter for steel detailing. 

Model space is just the original dimensions acc to the model and paper space which has the scaled drawing according to the sheets sizes and can prepare diff layout and title blocks in paper space

Scale in Model space is 1:1 and in paper space either we can use reduced scale or enlarged scale