What's the Bare Minimum of a CRM?

Some companies are heavy on the inbound lead flow as in you might have a self-serve mechanism where somebody signs up for your product and then they eventually become a deal. Other companies are pure outbound machines where you need to call somebody to get them interested. And some companies are a combination of both. So what are sort of like the canonical flows for each of those cases? For leads, let's just take leads and this could be for inbound and outbound. Now, once you engage with them, you put them into the contacted stage because you've contacted them. You're trying to get them to engage with you on a potential buying process.