...
The classes with format "f-<column number>-col" are used to apply the grid-column-templates styling.
The classes with format "col<column number>" are used to define the grid column start position and to be able to change column position when applying the responsive behaviour using CSS.
When you have a special use-case where you do not want to keep the styling as default for all the forms you need to use responsiveBehaviour attribute to apply a class on that particular form field.
...
Another example using the "xs-two-col" helper class, defined in the responsiveBehaviour attribute, which can be used for changing the columns template and positioning of the cells from inside blocks with multiple columns defined initially.
...