What is the exact use of IQService in Active Directory ?
On this link, you can find all the informations:
https://community.sailpoint.com/t5/Other-Documents/IQService/ta-p/158011
In short it allows to execute provisioning to AD World via RPC Protocol.
IQService functions similarly to a service on the AD side, allowing IdentityIQ to execute or perform the provisioning activities of a user from SailPoint. Without this IQService, you can also onboard the application and test the connection. But when you want to do provisioning from SailPoint, you must install it in AD.