Table to create Ids for one table to many table relationships
You could utilize a sequence object to facilitate the mechanism of generating the IDs if that is the sole purpose of the CommentParents table.  Take a look at the TechNet documentation for the TechNet SQL Server 2014 Sequence Documentation for more detailed information.  What this sequence object will do that your current table can't do is allow you to grab a value and assign it to a variable ahead of time without worrying about doing an INSERT/SELECT SCOPE_IDENTITY() process.  The advantage here is at great scale the current design you have would break down due to the need to maintain metadata overhead where SQL Server has caching for Sequence objects.