They just seem to be irritating little popups. What purpose do they serve?
Makes your inner child happy?
My inner child is so old that only a good scotch makes it happy.
I like them. 
Pavlov’s Dog.
There’s an ‘instant gratification’ thing at work. How many people post something on their social media page, and then … virtually hold their breath until the ‘likes’ start pouring in ?
It’s a little like Vegas, too, in that … anything they can do to get people to spend more time on the site (/in the casino) is good for their business model (eg, increased ad rates and revenues).
Think about why they added food courts to the shopping malls: no reason to (ever) leave the mall when your family goes out to shop.
Same-same.
It is weird, IMHO, but … then … I do tend to salivate a bit when a bell rings anywhere near me.
I have two more than you. Then again, you have a snazzy new avatar.
Beer outranks pipes.
In this reality, at least. 
Badges?
We don’t need no stinking badges.
Ummm, you have even fewer than Piper?!
I thought it was a mosquito
They (theoretically) increase user engagement, retention etc, especially (or specifically) for new(er) users. The principle behind their use is called gamification.
Philistine!
Interesting that most of my students (college, some high schoolers) are gamers. But they loathe badges, and will mock and even abandon sites that use them.
The only things that I roll my eyes at more are the intrusive Discourse alerts. F’rinstance…
(In the middle of a serious discussion):
“I used to cut myself until I found the right therapy.”
“Please wave at NOOSEMAKER97, they haven’t posted in 876000 hours! Everyone say howdy!”
“I just can’t stop.”
…
Is there any way to turn those off? If not, why not?
Meh. At first I thought it was a stylized hummingbird, and I thought “sandpipers don’t look like that, do they?” Then I realized it was a stylized bagpipe.
I’ve got a super-keen white square. That I don’t have to look at because of the theme I use (I wish there was one where I couldn’t see any at all, like on vBB).
Is there any way to change the minimum time from 876000 hours to 1 second?
Pretty sure they set it on purpose so people can always see if a post was deleted.
You’re correct. I’d just as soon they left us with the ability to edit a post to just say “nm.”
WITHOUT having to remember to add the HTML code at the end.
Because this way is just TOO wordy.
More than that - it was so the mods can read the deleted post.
Apparently once the tine runs out, the deleted post is gone forever, and even the mods can’t see it.
One of them explained that when the time was originally set to 24 hours, they got a report about a particular post, but by the time a mod had time to check it, the poster had deleted the reported post and it was completely Gone, so they had no way to review it.
By setting the deletion period to the max, a mod will always be able to check the deleted post.
you could type “no message”
or “nm…”