Discards are not complex construct but there's still one interesting use-case worth mentioning.
We can use discard when we use an operator that needs a left-hand side value but we actually do not care about. One of such operator is ?? - null-coalescing. To use it we need something on the left side as we can't just write
valueToProcess ?? throw new ArgumentNullException(nameof(valueToProcess));
but we can write
_ = valueToProcess ?? throw new ArgumentNullException(nameof(valueToProcess));
One just need to remember that _ is still a valid identifier in some context so it might produce unexpected results if one is not careful enough.