I don't think that !important is inherently bad in terms of how quickly the browser matches rules (it does not form part of the selector, only part of the declaration)

However, as has already been stated, it will reduce the maintainability of your code, and thus likely cause it to grow unnecessarily in size due to future changes. The usage of !important would also likely reduce developer performance.

If you were being really picky, you could also say that !important adds 11 extra bytes to your CSS file, this isn't really much, but I guess if you have a fair few !importants in your stylesheet it could add up.

Just my thoughts, unfortunately I couldn't find any benchmarks on how !important could affect performance.

I don't think that !important is inherently bad in terms of how quickly the browser matches rules (it does not form part of the selector, only part of the declaration)

However, as has already been stated, it will reduce the maintainability of your code, and thus likely cause it to grow unnecessarily in size due to future changes. The usage of !important would also likely reduce developer performance.

If you were being really picky, you could also say that !important adds 11 extra bytes to your CSS file, this isn't really much, but I guess if you have a fair few !importants in your stylesheet it could add up.

Just my thoughts, unfortunately I couldn't find any benchmarks on how !important could affect performance.