[kbhomes]

I can see the benefits of using @extend to clean up the HTML, but wouldn't this pull the .container, .row, .span*, etc. CSS rules into each and every rule that extend from those? Wouldn't that have a hit on performance and file size?

[timdorr]

I'm not sure how LESS handles it, but it adds your class to the selectors for that ruleset. If you do .myclass { @extend .container; }, you end up with .container, .myclass { // container styles }. It only adds minimal overhead.