Negative left and right margin of .row class in Bootstrap

Question

Just out of curiosity, why bootstrap uses -15px left and right margins which going to cancel the 15px left and right padding on .container and .container-fluid classes.
Why set padding and then cancel it with a negative margin on the child?

Answer 1

A negative margin on row avoids the blank space that would be left because of padding of first column. In its absence the whole layout will look a little indented.