<===> input.scss
$path1: assets/images; // no errors thrown
$path2: /images;       // errors thrown
.test {
  background: url(#{$path1}/image.png);
  background: url(#{$path2}/image.png);
}
<===> output.css
.test {
  background: url(assets/images/image.png);
  background: url(/images/image.png);
}