Based on MS documentation this is a quick way to create a copy of database (only Schema) including statistics and Indexes of source database this was released in SQL 14 service pack 2.
When this command is issued SQL Server creates an internal snapshot of source database just like how it creates for checkdb and drops this snapshot when the cloning process is done but during the cloning process it holds a shared lock on source database and X lock on target database and it leaves target database in read only mode although you can change the state of the target database if you intent to add data or modify.
So why do you need to clone database.
According to MS “DBCC CLONEDATABASE should be used to create a schema and statistics only copy of a production database in order to investigate query performance issues.”. The original intention of the feature is to diagnose any performance issues of a production database with out needing to effect the production database. Although this is so late in the game its never to late for new feature.
Don’t confuse with Database Snapshots that’s totally different concept.
Bottom line: Saves a lot of time when you are debugging execution plans and performance related issues.