Packaged into the Web Theme, and lifting from the base Bootstrap framework, are utility classes for showing, hiding, aligning and spacing content. This aids in responsive development within your layouts and can help mitigate mobile or tablet-related scaling issues.
Most of the Bootstrap utility classes will work with the Web Theme, although your mileage may vary. Below is an example of a Bootstrap class, 'hidden-sm', that is used to hide this blade for mobile devices:
Also, utility classes can be extended through custom development or the addition of 3rd party Drupal modules to your Web Theme site. Typical use cases for this field is hiding things like icons for mobile users, as it doesn't add or subtract from the content in a smaller width device.