In which scenario should a marketer use inventory packages?

A client in the travel insurance business wants to create a custom ad unit to put on the homepage of a few top travel websites.
A client in the music industry wants their new album to reach as many listeners as possible while maintaining an efficient CPM.
A client in the trucking business wants to have an ad deal with a publisher and the flexibility to cancel the deal if weather conditions impact their business.
A client in the wellness industry wants to execute non-guaranteed inventory with many health publishers.