Answer by Izquierdo for How to handle separate Design Systems for B2C and B2B from one company

I can think of a few arguments against having two separate design systems:

1. Duplication of effort - You risk rebuilding things that already exist in one system or the other
2. Precedent - You're showing the organization that some products are allowed to not adopt the core design system. You'll hear a lot more "but my product is also special and deserving of its own design system"
3. Brand divergence - Instead of creating products that look like they belong in the same family, you're risking having one team go one way and the other team go a vastly different way. The point of design systems is to prevent this.
4. Resources - If resources become reduced, one or both systems might become hard to maintain, and one is likely to wither while the other receives priority

So in most cases it's better to have one core design system file, with components and variants that support different cases. A good example is developer portals - lots of core elements and patterns shared between a company's marketing site and the dev portal, serving very different audiences, but they stay bound together through the same elements.