I wouldn't think of buying a 512 GB SSD for a workstation, let alone a Macbook Air. That's not future proofing, it's a waste of money.

It's also not about "storage". It's quite simple to get "storage" with external HDDs, as noted in the OP. What we're talking about here is paying for premium onboard flash storage, which is unnecessary, particularly on an MBA.

I've been using an Air as my sole computer since 2010. I just upgraded to a new one, and spent the $300 extra for a 512G SSD. My old 256G machine has been hovering close to full for the past few months, which has been pretty annoying when I tried to do things like "prepare a 120p graphic novel for printing" or "edit a video for that GN's Kickstarter campaign". I dug out an old external HD for those purposes, and really hated that I was using one - I had to do these things at home now.

I want to have all my data available when I go on a trip, or out to a cafe. And I don't want to hassle with carrying external drives or finding power for them; that completely negates the "lightweight" and "has a long battery life" features of the Air. Which were the major reasons I switched to one.

Obviously you don't have any need for that kind of space - but trust me, there are people out there who do.

Have to disagree. Different people have different use cases and different budgets.

In particular, some people might like the mobility of the MBA, but have a lot of photos, music, or movies they want to take with them (i.e., different use cases). And many people have the means to shell out for large internal storage because they don't want to manage the external drives. Some people like Kias, some like Lexus.

Actually, I would argue that external USB disks are more annoying to use with a MacBook Air than with a workstation. I couldn't even have my MBA on my lap right now if I had to connect an external disk for music or apps.