Sorry, but I strongly disagree and I feel you're missing the point of BEM and about my initial question.

To get back to my initial question and your two cents: 1. Bootstrap shouldn't be hard, in fact, if you don't know CSS, you shouldn't be using Bootstrap. Bootstrap is nothing more than knowing where to put CSS classes, there's nothing to learn. 2. Again, I strongly disagree. Will it make development time easier for projects where you don't want a custom layout? Yes. Otherwise? No

Bootstrap adds so much default stuff to their framework that you'll end up overwriting so many styles when you're working with a custom layout. 3. Bootstrap is a framework, BEM is a mehodology (i.e. a way of thinking), Sass is a preprocessor that makes it easier to write CSS.

In fact, there are many new things, writing CSS with Sass is not just about putting duplicate styles in mixins, because when it's processed, it's just duplicated again. 4. There's nothing to learn about bootstrap.

To get to what you said: BEM and using presentational classes is all about re-usability, in other words, writing CSS that is re-usable and not specific to one thing.

Using class="login-button" is terrible, it's most likely your login button looks the same from any other button, except that it might have different colors. Using Sass won't help you with that.

In fact, this is a problem many people encounter with Sass, they start to use mixins without actually realising what they're doing. Creating a mixing to style a button is just bad practice, your duplicating so much CSS.

The reason Bootstrap uses btn btn-default is because they're following the BEM methodology, i.e. going for re-usable code.

Anyway, I would be happy to discuss further, I've been involved in many large front-end projects and have written quite a few custom frameworks for companies. (Btw, I'm not attacking you, I'm just suggesting different ways of looking at things)