With tethering, I'm not sure I want a SIM card in my laptop! If nothing else, AT&T will charge me extra for that (I'm already paying extra per month for my Apple Watch to have LTE connectivity).

Whilst I don't take my phone running because I can use my Watch for music and can make calls on it while out, I don't think I'd ever be somewhere with my laptop and no phone.

The problem with that is that MacOS has no concept of “low data mode”. If it has a connection, apps are going to use it. You can deny apps from being able to use data over cellular on iOS. Also, well behaved apps will usually give you an option to either not use data or in the case of streaming apps, use less data.

What you say is true.

It is also true of tethering, which is quite popular.

Now, I can tether my phone to my laptop. Indeed I did so fairly often, before global house arrest.

But this is true of my iPad as well, and I opted for the cellular model instead. I'm glad I did, it's a better experience, hands down, especially when I'm traveling and want to conserve my phone's charge rather than burn it at maximum.

But if you felt differently, Apple sells a WiFi only iPad, you could simply not pay the extra for the cellular model when checking out. This would almost certainly be true for this imaginary Macbook as well.

I wouldn't buy it at all, I'm a professional developer with mild presbyopia, and purchased the standard-fancy model of the 16". But if I were an incoming freshman again? Bet I'd be pleading with my parents to get the cellular model.

Unlike a touchscreen, an LTE modem doesn't demand any changes to a desktop operating system to provide a good user experience. Again, tethering. Cell bandwidth gets cheaper every year.