The main benefit of using Sass in CakePHP web development is its flexibility. Sass allows developers to easily create complex, nested style rules that would be difficult to replicate using traditional CSS. This makes it easier to create responsive designs and build websites that are more consistent across different devices.

Sass also provides a number of helpful features that are not available in regular CSS. For example, developers can use variables to store and reuse colors, sizes, and other values, making it easier to update multiple elements of a website at the same time. It also supports the use of mixins and functions, which allow developers to easily create complex effects.