C#: In what cases should you null out references?

Question

The CLR Profiler can also reveal which methods allocate more storage than you expected, and can uncover cases where you inadvertently keep references to useless o

Answer 1

It's important if you have long lived objects (like the cache example in your quote) holding references to short lived objects (like the cache items). Other examples of long lived objects could be singleton objects, the Main Form instance in a Windows Forms application, the Application instance of a ASP.NET application etc.

I would like to add a another common pitfull: short lived objects subscribing to events published by long lived objects. As the event publisher holds a reference to all subscribers, the subscribers (like e. g. ASP.NET page or control instances that are needed only for milliseconds) won't be collected if you do not unsubscribe.