The only thing they're going to do is open it as an ifstream. Zero value is gained over taking an istream instead; initializing it is one bit of extra code for

The only thing they're going to do is open it as an ifstream. Zero value is gained over taking an istream instead; initializing it is one bit of extra code for the user, in exchange for being able to pull in data from anywhere. Embedding it in the binary might be rare, but how about stdin? Or for that matter the Internet?