why we use offset in bootstrap code example

Example 1: col offset in bootstrap

.col-md-3 .offset-md-3

Example 2: bootstrap offset

<div class="col-sm-6 col-sm-offset-3"></div>

Example 3: offset bootstrap

$grid-breakpoints: (
  xs: 0,
  sm: 480px,
  md: 768px,
  lg: 1024px
);

$container-max-widths: (
  sm: 420px,
  md: 720px,
  lg: 960px
);