second source

Acquisition or procurement strategy where two producers or suppliers are qualified to supply the same item.

It's always beneficial to have a second source, or at least a second potential source, for any products or services you need to run your business. Without it, you become too reliant on the single source and this can hurt you in several ways: if the source's business changes that affects you in ways you might not want; if the source knows you don't have a second source that weakens your ability to negotiate favorable terms; etc.