Whenever you want to digitize something, you need to start with designing processes. Digitization usually requires some piece of technology, and you need to “tell” the machine/software what it is supposed to do, i.e. which actions to take under which circumstances – and this means designing processes.
Also, digitization often means automating at least some of the actions, so that, ideally, they can be scaled quickly. After all, that is one of the main advantages of digitization. And automation, of course, requires predesigned processes (otherwise you cannot automate).
Even in a broader sense, when, for instance, designing a platform business model, you need to carefully think about your process design. Which processes do you want the platform to support and how exactly are these processes supposed to work? Well, it all starts with processes.