Dennes Torres gives us a reminder of what the world was like before a new feature in SQL Server 2019:
Once upon a time a SQL Server version that hadn’t row locks. The minimal level of lock was page lock, every time you want to lock a record, an entire page was locked.
At that time we were between the devil and the deep sea: if we choose a clustered index with an ascending key we would create what was called a Hot Spot, all the records would be inserted on the same page, creating a bottleneck. On the other hand, if we create a clustered index with a non-ascending key, we would suffer from index fragmentation and page splits, having huge admin trouble to find out the correct fill factor for each index in order to support the period between the re-index job without too many page splits.
Dennes covers the specific case which this feature intends to cover and how we got there.