A data point from a forum that runs into this constantly.
I administer a smaller forum with a classifieds section. Across its for-sale, wanted and trade categories there are 12,343 topics. Of those, 5,669 (46%) have never received a single reply. Only 2,609 (21%) got a reply within the first 24 hours.
I think that supports @Ethsim2’s narrower version. The two conditions in can_delete_own_topic? test different things, and only one of them tests what we care about. posts_count <= 1 asks whether a conversation exists. The 24 hour timer asks nothing: at the moment it expires, 79% of our listings have no reply, and 46% will still have none years later. Its practical effect is to take a permission away from the authors of topics that nobody ever answered.
The everyday case is a listing whose item has sold. The author wants it gone. They can edit the title to “Sold”, or flag it and wait for a moderator. Our moderators do the second one by hand, which is make-work on both sides.
One oddity, rare but strange. Last week a moderator replied to a listing to ask the author for a clearer title. That reply took posts_count to 2, so the author permanently lost the ability to withdraw his own listing and had to ask staff to do it. Only 26 of our 6,674 replied-to classifieds topics have staff-only replies, so this is an edge case rather than a real problem, but it is odd that a moderation note revokes an author permission.
A site setting for the limit, defaulting to 24 hours and leaving posts_count <= 1 alone, would cover all of this.