Why Castbar.IsCast Exists?

[ACastanza]

So this table Castbar.IsCast seems to be used as a whitelist for which abilities should create a castbar. It seems like this table contains a near comprehensive list of all abilities with a cast time in the game. On top of this there is a separate API function

channeled, durationValue = GetAbilityCastInfo(abilityId, overrideRank, casterUnitTag)

(note small syntax change from live version, this version is PTS) being used that tells you if the ability has a cast time already.

Removing the check for this table doesn't seem to cause any issues with the castbar. Is there a specific edge case that this was created to address?
There is also a separate CombatInfo.SV.blacklist table, might just using the ignore list (moving it into CastBarTable) and removing the check against the IsCast table be simpler?
It would also prevent us from needing to add every scribed ability variant that has a cast time to this table.