Benefits: 

• Meeting more like-minded people sooner 
• (For people serious about academics) In some fields (like AI), learning is faster and more efficient if if the teachers are active researchers. You can do research as an undergrad.
• For people focused on work, you can start working earlier and so it's easier to try more jobs/internships. (Many jobs require BA/MA and so you can't do as much of this before starting uni). 

Also, the Bay Area is probably the top metro area in the world for AI capabilities R&D (because of Google, OpenAI, Meta, various ex-Brain startups, Stanford, Berkeley). So if starting from scratch, there'd be a good reason to put AI Safety orgs there. 

>In many countries, people start their university education at a younger age than Finland.

IIRC, Finns start university at 20 (or later if they take gap years). My sense is that many people who are strong academically could benefit from starting at 17 or 18. If that's not possible in Finland, I'd suggest people consider applying elsewhere (EU is often free, US/UK is expensive but worth it for many people). 

In the Bay Area, it's very common for younger people to share accommodation (and not an alternative lifestyle). But this is often a set of somewhat random people living together and not an intentional group house of like-minded people. As people get older and have higher incomes, people are less likely to share (AFAIK). 

So EA group houses do indicate an alternative lifestyle ... but in places like SF and Berkeley such alternative lifestyles are also pretty common outside EA.

Many cities many EAs live in have very high living costs. Thus, even full-time working adults often do flat sharing. This is why some people have set up EA (or rationalist) group houses: they’d prefer to live with like-minded folks.

This is only partially true. There are many EAs living in group houses who could afford to live alone but prefer group houses.

I'd expect it to be harder to tell that Russia is heading towards nuclear war than that they are planning an invasion.