Why a named process, not a general principle
Process & Workflow and Business Automation cover the principles: how to map a process, how to decide what's worth automating, how to work out the cost. Those apply to any process you run.
Workflow guides do something narrower and more concrete: they take one specific process almost every business has, client onboarding, invoicing, following up a lead, and walk through its actual shape. That's useful because the generic advice ("map it, find where it sticks, decide what to automate") is easier to apply once you're looking at something that already resembles your own process, rather than starting from a blank page.
How to use a workflow guide
Read it looking for the differences, not the similarities. The steps that match your own process confirm you're on the right track. The steps that don't, a stage you don't have, an extra approval the guide doesn't mention, a different order, are usually where your actual opportunity or your actual bottleneck is sitting.
How these six fit together
Four of them chain together for a typical client-facing business: a lead gets followed up, turns into a quote, the quote gets accepted and the job runs, and the job being marked complete is exactly where invoice approval picks up. If the client's brand new, client onboarding runs alongside the quote being accepted. Employee onboarding and expense approval are internal, they don't depend on where a client is in that chain, but they tend to break for the same underlying reasons as the rest: a handoff nobody owns, or a step that depends on someone remembering.