Conflicting messages about headspace

I'm completely new to brewing, I haven't brewed a thing yet. I'm basically just here doing a bunch of research before I actually start. One thing that I'm unclear on is the amount of headspace that should be left in the carboy/fermenter.
I've read many people say in many places that you want to leave as little space as possible, but I've also read that if there's not enough space, then a busy fermentation will likely require a blowoff tube, and possibly even clog that up with kreusen.
My expectation is that it's a complicated answer that involves the phrase "it depends."

The different information you are getting is just a result of different schools of thought. Some people like to have it blow off and get rid of the kreusen, some don't. Both is just a matter of preference, your beer will be good either way. I'd recommend using a blowoff tube on your primary no matter which approach you choose. I keep a lot of headspace, but still always use a blowoff tube, because it's pretty ugly when it blows off and you don't have a tube.

The only time it is essential to go one way or another is when you are doing a secondary-- you want as little head space as possible there, because the head space is oxygen and your beer has already fermented, so you want to limit the exposure. In the primary, oxygen will get expunged when the fermentation's CO2 pushes it out. Your research has/will point out that a secondary isn't going to be necessary for your first time.

5 gal batch in a 6 gal + bucket is best for primary.. The 5 gal bucket is used as a secondary... but most don't bother....including me

Primary fermentation: you want a fair amount of head space to account for how high the krausen will rise. Depends on the yeast strain, temperature, and OG among other things for how much you'll need before you start experiencing krausen out the airlock.

Secondary/aging: you want as little head space as possible. No actual fermentation should be taking place at this point, so relatively little, if any, CO2 coming out of solution and making the head space a fairly anoxic environment like in primary fermentation.

That's how I see it at least.

I'm mostly interested in mead, which (from what I've read so far) pretty much always have secondary's. If it makes sense to have extra headspace in the primary, and very little headspace in the secondary, then it was probably just my inattentiveness that accounted for not noticing that the different people advocating for each were also talking about different situations.
That makes a lot of sense. Thanks.