Be very wary, though, if you are using mixins to define these columns in a case-by-case basis, as this could lead to huge generated CSS (the properties of the column will be defined in each class the mixin has been used).
Thank you so much for pointing this out, Moretti! It drives me crazy when people talk about the extend feature like only SASS has it. People are always underestimating how similar Less and SASS are.
i.e. if you have:
And you do: Then the generated css will be something like: [1] https://github.com/twbs/bootstrap-sass