> ULA give more trouble than what it solves.
How? They're essentially the same as IPv4 addresses; the only difference is that there are way more of them, so address conflicts are much less likely.
> Almost all computer have multiple interface (virtual or not)
Sure, but that's the case with IPv4 too: my cell phone has one IPv4 address over WiFi and another over cellular, and my laptop has one IPv4 address over WiFi and another over Ethernet.
Edit: Ah, I think that eqvinox's comment [0] is what you were getting at here. And yeah, I agree that LLAs are kinda confusing and annoying. The difference is that LLAs aren't routable [1] and don't have an IPv4 analog, while ULAs are routable and are mostly equivalent to IPv4 addresses [2].
[0]: https://news.ycombinator.com/item?id=47814154
> LLAs (...) and don't have an IPv4 analog
They do. You don't really see them on Linux unless configured manually, but Windows defaults (or at least defaulted in the past, my Windows-foo is very outdated by now) to a IPv4 LLA when DHCP fails.
The difference is that IPv6 requires it on every interface regardless of whether it has a different address already.