If a site has a large set of TXT records, they can be used by clients that spoof packets to request large volumes of answers by DNS servers. This is called an amplification attack. Many tiny spoofed requests in, many large answers out.

What is this altchan.org place? Looks very new. Where's the reply button?

Its just a private fork of an open source anonymous image board. I had a static blog for it but I got bored and moved all my blog posts to the image board. Probably a rather unorthodox experiment. The reply button is at the bottom right. I might change that.

And why do we want finger to exist?

There were discussions in the past about the finger service and how hardly anyone runs it any more and even less likely to be found on the open internet. DNS seemed like a good replacement for it to me as more and more people have domains now and authoritative DNS servers are likely to be more secure and distributed I think. Maybe one day specific groups of people do something like this in place of sites like X. half kidding

Now instead of having a special purpose client, one need only query a DNS record. In this case I use "dig" as the example but there are other DNS tools people might prefer to use.

Because it allows for an easy interface to see what someone else is up to without needing to load a JS-heavy page.