I have the same question. I keep seeing it in other developer's code, but like you I thought it was unnecessary. I thought the only objects you needed to address in the finally clause were ones that implmented IDisposable or interfaced with unmanaged resources.

It is habitual programming. There is no need to set a *local* variable to nothing, as the reference will be wiped off the stack when the function ends and unwinds the stackframe. Assuming the heap object data for that reference has no other references, the GC will take care of it later.

However, your Finally block *should* properly call Dispose or Close for objects containing unmanaged resources. Only a percentage of objects have a Dispose or Close method, so it's not something you have to do for everything, and certainly not for entirely-managed objects that you write.

Also, for performance reasons, it sometimes can be better to release the managed resources as soon as possible. How much gain you get? I'm not sure.