One problem we have on our service (genenetwork.org) is stylistic consistency across many different pages and forms. Even one programmer can invent five different ways to close a window or pop-up. Table styles can be annoying diverse.

A style guide is the obvious solution but ……

I turn this into a design one time. Everything had a different Color scheme too. It was oddly usable with the colors setting the mindset.

It depends a lot who the audience is.