I agree one physical box can do a lot. As you say though, if you want HA/DR now you're already expanding beyond a single box. You're likely talking multiple box

I agree one physical box can do a lot. As you say though, if you want HA/DR now you're already expanding beyond a single box. You're likely talking multiple boxes in multiple locations. Now you have to think about how your data is potentially replicated across. You have to think about monitoring. You have think about how you upgrade your software and maintain your services. You have OS/package upgrades. Where do you test? Do you have a staging environment? How do you monitor all this stuff? Does your business only have this one app or does it grow to offer more apps? Internal services? I'm sure plenty of things fit this model. But many do not. There's going to be a point where you're taking more pain if you chose the wrong model.