Example: This recent post from P&R.
The URL appeared for like half a second for me (it was a tweet, in case you didn't see it) and then it just disappeared leaving empty space instead of a box with some kind of 404 error inside like I've come to expect from most forums. With no obvious indication that there's supposed to be something there, posts with broken embeds could be very confusing.
EDIT: Oh ho, the plot thickens. When I follow that particular link to the exact post, I actually do get a broken embed box, albeit a really ugly one, but when I just load the page by its page number, it does what I described.
The URL appeared for like half a second for me (it was a tweet, in case you didn't see it) and then it just disappeared leaving empty space instead of a box with some kind of 404 error inside like I've come to expect from most forums. With no obvious indication that there's supposed to be something there, posts with broken embeds could be very confusing.
EDIT: Oh ho, the plot thickens. When I follow that particular link to the exact post, I actually do get a broken embed box, albeit a really ugly one, but when I just load the page by its page number, it does what I described.