All else equal, URLs that present consistent content are better than links where the content changes arbitrarily over time (making an exception for e.g. the front page of some list).
Some use cases:
(1) Start skimming through recent notebooks from sequential pages. Go away for a few days. Come back to the page and pick back up where you left off, instead of needing to scroll all the way back down from the top.
(2) See a few interesting notebooks that were published at about the same time. Email the link to your buddy, and have it still be valid a few hours later
(3) Enter some date in the past and see what kind of notebooks people were publishing on that day, instead of needing to guess the page number for that day.
Something not on Observable per se, but I find those infinite-scroll-with-no-URL sites incredibly annoying, and one of the big reasons is that there’s no kind of permanent URL to a point in the stream.
If I navigate to e.g. https://twitter.com/jashkenas and start scrolling down through the top 50 entries, and then I somehow navigate the browser away, there’s as far as I know no way to get back where I was without scrolling down from the top again. If instead the URL were updated to indicate the date of the tweet I was just looking at, I could go back to that URL at any point to pick up reading the stream.
If you have a page of search results for some complicated query where the order is not chronological and will change arbitrarily over time, then making a meaningful stable URL gets harder. In theory you could attach the date to the URL and as part of the search query filter out all newer results. But making those pages stable takes more thought and work, and might not be worth the engineering effort.
But for stuff that’s just “show me X page of stable results taken out of an append-only ordered list”, the URLs which keep track of the exact position in the list instead of just the position relative to the recent end are much more useful. YMMV.