Not the GP but our example is we have a lab (chemistry lab with fume hood etc). But nobody has to go there every day; it’s used 2-3 days a week.

The facility has some cubicles and conference rooms as well. I go in when someone’s in the lab and work in one of the cubes (sometimes I assist in the lab since I’m qualified to do so). But most of the work can be done remotely (including data analysis, so why drive in? We have a remote culture that works for us so going in isn’t that different than going to a field site.

Probably collaboration hubs, client meetings etc.

Not the OP but something like a hardware / chemistry lab or the need to comply with government-classified secret protection would be a good reason. Basically, stuff that you can't legally and/or reasonably do from home, or from other countries.

Additionally, in some jurisdictions regulations require that certain kinds of documents - mostly HR and finance - are to be kept in offices as well.

If you need manufacturing facilities, a workshop, or a lab, having a central office still makes a lot of sense. You can't ship every engineer tooling and equipment that costs 5x their annual salary, and they probably can't bolt it down or power it up in their home office.

I do prefer working remotely when possible, and can do so ~30% of the time, but when I'm needing to cause motion in a $500k CNC or $50k robot I really ought to be on-site, physically watching the equipment and physically checking wires. But if I'm just copying data from a PDF to Excel, just writing emails or sending Teams messages, or just programming a PLC or HMI (or, like most startup devs, programming a cloud-based webserver), I don't need to be physically present until the final commissioning. Send engineers home with a laptop and maybe a test bench or dev kit, don't expect them to have a full manufacturing office.

But hardware is hard and hardware startups are relatively rare.

If you're doing any work on classified (secret) materials then those have to be kept inside a secured facility. HN comments tend to ignore such issues but in the real world this is a huge industry.