What explains the negative padding or magrin in Boostrap meshes?

Question

css

The container class has a padding of 15px
The row has a margin of -15px
The child classes col-* again have a padding of 15 px The
question is:
Why does container have 15px padding, if it was possible to leave them only for col-* . and .row should not have negative margins at all?
I understand that all this is not just like that, but I still do not understand the essence of what is happening

Answer 1

In order for there to be an indent between the two blocks, but not between the block and the edge of the page.