From my experience: Better have a > 32gig USB Flash drive, everything else doesn't work (MSI) and I don't have an UPS so it's always quite an exciting experience. Especially since Motherboard Manifactures save almost a whole dollar by not having a display ouputting anything. So it's blinkenlights and hope for the best
Not just for convenience, but safety. You don't want to be caught out when something goes wrong, even without flashing the bios.
A lot of boards these days have 7-segment displays. They're not great, but they're a good step up. Don't need to spend a lot, I think they show up on $300-ish boards. Mine definitely does.
I see no need for it. Living in Germany, any kind of power outages are exceptionally rare. I remember one in the last 10 years for a few hours and that was very local. If I am in a situation where a power outage occurs, i'll listen to my battery radio for a while and be fine. I work on nothing and rely on nothing that would actually require a UPS.
It's like not having a backup drive. Everything is fine until one day it isn't.
A good UPS does more than just protect from outages. It also protects from surges and low-voltage situations that can both damage the equipment severely.
A UPS doesn't cost much and will last many years. Buying a new motherboard and GPU because they got fried is much more expensive.
Keep in mind that most equipment of this nature has universal power supplies, and thus works even at just 50% of nominal grid voltage.
The substation is mandated to trip in that anomaly, btw. Otherwise some very common types of motors (AC induction, single and 3-phase) would burn from the excessive current they draw to compensate for the reduced voltage.
