There are junctures where a strategic partner is critical to growth of a business. For example, you have developed and patented a widget that provides activity related information of the wearer to their doctor. This widget can be attached to a shoe. While you could sell this to sporting goods stores globally, it may be more beneficial to partner with a known athletic shoe brand whose reach is far wider than what you are likely to have for years, and they have the funds to be able to buy substantial quantities.
At a point like this like this, the athletic brand may be willing to invest in your business because you have demonstrated that you can evolve the product to provide more than just activity readings in the future. This creates an environment of synergies – you need the funding to continue R&D and they need your widget to enhance the Unique Selling Proposition of their shoes.