It is important for product teams to build a design system for two reasons. It’s way easier to update and maintain the product if the team has a set of guidelines that are followed consistently. It may sound like a small thing to have a design language, but when you have a complicated product/site, consistency is a huge win. It’s easy to forget what you’re building, or get on the wrong track when the team isn’t all on the same page.
A design system is a collection of design, style, and pattern libraries. In the past, they were a luxury. Today, they are a necessity. The design rules, patterns, and elements that made sense for one project are no longer relevant for another. Building a design system allows developers to share iterative design knowledge, and allows designers to build on patterns and code that have already solved a problem. This shared knowledge can be leveraged across a team and project.