Great resource for lead generation and prospecting - strongly recommend.

[ZoomInfo is] great as a lead gen and sales prospecting tool, for insights into a business and understanding their calendar of events, general business intelligence and insights. Any opportunity to gain an insight into an unknown organization.
Where it wouldn't be useful - any sort of client management approach or any scenario where you have easy access to the internal workings of an organization. ZoomInfo is only useful as an outsider looking in.