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> 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 object graphs that otherwise could be reclaimed by GC. (A common problem design pattern is a software cache or lookup table of items that are no longer needed or are safe to reconstitute later. It is tragic when a cache keeps object graphs alive past their useful life. Instead, **be sure to null out references to objects you no longer need**.) -- [Writing Faster Managed Code](http://msdn.microsoft.com/en-us/library/ms973852.aspx)
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I don't think I've really ever nulled out a reference before. I assume you don't always need to do this, but I guess there also are times when it is important to remember to do it. But, what cases is that? When should you null out references?