The advice in here is good for not just authors. App developers and film/TV producers should know about it too.
Here's an example of the clause in question:
The Work contains no matter that the publication or sale of which violates any law or regulation, nor is it in any other manner unlawful, and the Work will not violate any statutory or other copyright or any other right of any third party (including, without limitation, rights of privacy, rights of publicity or moral rights), or be libelous or obscene, or in any way illegal.The author notes, and I agree with him, that this clause can have very far-reaching consequences. Read the post, even though it's long, because it's totally worth it.
The original post