As can be seen at https://wow.gamepedia.com/API_C_TaskQuest.GetQuestsForPlayerByMapID
this is also used for some dailies and combat ally quests.
Can be witnessed especially in Nazjatar, Mechagon, Valley of Eternal Blossoms and Uldum with 8.2 and especially now with 8.3

It seems to be used for "Quests of Interest" like important story line events like the warcampaign to help players find the next chain.

How about we make the API into a new Wholly sub menu with the MapID&MapName in the tooltip?
Categories across all maps for isDaily, IsCombatAlly & IsQuestStart would be nice in general and especially for analysis.

I am going to have to play around with this a bit because during some basic testing in Uldum I see that it returns both 1527 zone quests (modern Uldum) and 249 zone quests (old Uldum), but in 249 those quests do not exist. Also, the quest to go into the madness for Uldum today is not returned in the list. But I will see about incorporating this as best as possible.

I am not sure exactly what isQuestStart is about, but it may be the golden quest icons that show you important next hubs. Still haven't found a valid example of that bool being true