Can a page have multiple ScriptManagers? If yes then under what condition will it be required?

Question

Can a page have multiple ScriptManagers? If yes then under what condition will it be required ?

Answer 1

MSDN says no, you can't have more than one (emphasis mine):

A page can contain only one ScriptManager control in its hierarchy. To register services and scripts for nested pages, user controls, or components when the parent page already has a ScriptManager control, use the ScriptManagerProxy control. For more information, see Using the ASP.NET UpdatePanel Control with Master Pages