Which of the two expressions is correct? Is there any difference
This might turn out unnecessary.
This might turn out to be unnecessary.
They're both perfectly fine and grammatical. Some people may argue that the first example is a bit informal. However, here are lots of examples of turn out unnecessary from Googlebooks.
This usage directly mirrors turned out fine and other such common and clearly idiomatic examples. I tend to think the more technical the adjective concerned, the less likely we are to use the first structure. Though, this is just my personal opinion. The theory is somewhat supported, however, by the fact that there are a much greater number of examples of turn out to be unnecessary than turn out unnecessary. Conversely turn out fine is much more common than turn out to be fine.