I wanna talk about nothing.

I think it's a useful thing to consider.
Nothingness as a temporary state, as in an absense of a predefined thing (whether that is 'all matter' or just 'anything of note') is just as useful and important to us as the concept of absolute void is. The more tangible has obvious uses as you stated with the numerical thing, or the fabled mythical empty parking space, or the last open slot in a server. But also things that are harder for us to comprehend, like vacuum, which are also physical and non-permanent. Absolute nothingness is mostly an abstract concept that we use as a placeholder for lacking better understanding, or for when we create a kind of mental bluescreen when we mix our syntax contemplating things. Its kind of like when people ask the meaning of life, and I point out that question is too vague in its shortness, making it about as useful to ask as "What is the speed of velocity?" or "What is the pitch of sound?". Or trying to comprehend what it would be like to experience oblivion (as in, total removal of consciousness or sense, the most common atheist death expectation), when by its definition such oblivion cannot be experienced.

For how intelligent we can be, sometimes our curiosity requires us to be briefly really dumb while we mentally construct a means of comprehending the big stuff, haha. It's still fun to grapple with such things, even if it can give us jolts of existential dread.

Now if only people could try to remember this mentality and occasionally remember to approach social or political matters with a similar attitude. Like, not all the time, just occasionally giving ourselves a brief deep-check on our behaviour, assumptions, attitudes, etc. It's similarly difficult and will cause similar moments of dread, just not the existential kind. Nothing sucks more than realising you had grown a bias or were hanging onto something that isn't necessarily true, but the upside of this is that the sting of realisation can be quickly replaced with the relief of straightening ourselves out.

This is why I'm a fan of meditation. These kinds of conversation are fun but we have to let ourselves to adopt a certain frame of mind to appreciate them. Yet when we're out there on our daily grind, we hit a kind of autopilot that doesn't lift easily, and we forget to question, or at least forget that the answers we find aren't necessarily the cutting edge of truth.

Sometimes the important thing isn't a definitive conclusion. Sometimes the important thing is just to have the thought, the realisation, or the vaguely related memory. That kind of present mindfulness might not always yield results but it at least creates opportunities for them that we wouldn't have if we were just constantly outputting our opinions without pausing to stir our gray matter and occasionally make new opinions with fresher ingredients.

So uh.
I dunno where you were going with it either. But it looks like I joined you and decided to forget if I had a point too, haha :P

We look at dots in the sky, dots that are far far away, and if we look again much later at those same dots, they moved!

It matters because billions of years from now, when we as a species are most likely long gone (though the robotic or energy entities we created might still be around, they are bound to figure out how to reproduce and make us obsolete) the universe will reach a point where it can't expand anymore. Think of it is a rubber band or a piece of gum, it can only stretch so far before it snaps. In the case of the universe the snap will mean everything will get so cold all processes cease...or hot....or inactive...

https://www.youtube.com/watch?v=4_aOIA-vyBo Kurzgesagt.

Okay, but does it really matter though? I dunno, humans are innately bored...or was it curious....or scared? So we look for order in the chaos.

What if in reality everything is getting smaller except for the outer limits?
Things shrink but it looks like expansion because the distances between things are growing.
If 1 atom shrinks 0.00000000001% percent you can't tell, but line up 100000000000 of them and you'll notice your chain is shorter by 1 unit. But if everything shrinks...so does your ruler :P

(I know this doesn't work, something will burst :P)