Purpose of using ViewModel in MVC

The one and only purpose of a Viewmodel class is to contain (strongly typed) data to be sent to a view by an action method.

So as the answers in your referred question suggest create a Viewmodel class which contains properties for all the data you need in your view.

The advantage of Viewbag usage is that you don't have the overhead to create a separate class. The disadvantage is that you don't have compile time type checking and intellisense available.