Comment by csense

DNS is something you rarely change that has costly consequences if you mess it up: It can bring down an entire domain and keep it down until TTL passes.

If you set your TTL to an hour, it raises the costs of DNS issues a lot: A problem that you fix immediately turns into an hour-long downtime. A problem that you don't fix on the first attempt and have to iteratively try multiple fixes turns into an hour-per-iteration downtime.

Setting a low TTL is an extra packet and round-trip per connection; that's too cheap to meter [1].

When I first started administering servers I set TTL high to try to be a good netizen. Then after several instances of having to wait a long time for DNS to update, I started setting TTL low. Theoretically it causes more friction and resource usage but in practice it really hasn't been noticeable to me.

[1] For the vast majority of companies / applications. I wouldn't be surprised to learn someone somewhere has some "weird" application where high TTL is critical to their functionality or unit economics but I would be very surprised if such applications were relevant to more than 5% of websites.