In simple cases `&` is just replaces by parent selector (Like in SASS or LESS), only some cases are treated as BEM nesting (pseudo-selector that doesn't exist,

In simple cases `&` is just replaces by parent selector (Like in SASS or LESS), only some cases are treated as BEM nesting (pseudo-selector that doesn't exist, etc). If you use SASS or LESS and happy with them, you don't need BOSS. But you may take a look at it, 'cause it has simpler syntax for mixins and variables, which is more CSSy. So BOSS is more like a superset to SASS and LESS, their features + some new stuff + simpler syntax.