Style guides can be beneficial to your development process. Most sites that I see worked on do not have a base style guide set up for them for all of the different elements on a webpage. You can find an example of what I am taking about here.

Granted, not all HTML elements will be used on the average site, but it can still be a great thing to test your styles against a single static page for a sanity check if you notice some weird styling happening on your site. Some developers might argue that this would be difficult with the type of site they are building due to multiple module types, and style rules changing out based on what modules are being used. I believe it might be a bit trickier to implement, but it can in fact be done...

I have seen an excellent solution on a project where the developer utilized Gulp to break out each of the different Handlebars templates being used, and with the help of Assemble, create a great site outline that showcased all of the different modules being used on the site. This would automatically be updated when the developer changed any Sass or HTML partial, and the output generated was easily passed off to the client for their review and reference. This is a great use case for leveraging your build process to output something else other than your normal asset flow.

While not the most amazing thing, small items like this added to projects really go a long way when turning over code to a client for them to implement.