Think is like the most "functional" way to do CSS, in contrast with the "OO" way (like bootstrap).
Each class is applied in pipeline.
And ONLY to that tag. This is key. This leads to know, exactly, what are the effects on each tag, making the UI design very readable.
Then, you can customize it, and have a way to generate a VERY small CSS as result (another big advantage!) because the naming is normalized.
In short: Is the "same" but with more structure, predictability and tooling applied.
The more you need to customize, and the more pain you to "reverse" a CSS made by others, the more this make sense.