When should the benefits of quantitative risk analysis be weighed against the effort required to...

The Plan Risk Management process is where the project team determines the depth and breadth of risk management activities, including whether quantitative risk analysis is appropriate. PMBOK® Guide says:

"The Plan Risk Management process determines how to approach and conduct the risk management activities for a project. This includes weighing the benefits and effort of advanced techniques such as quantitative risk analysis."

— PMBOK® Guide, 6th Edition, Section 11.1