Why do we use stringstream to pass data to ofstream in c++

I happened to find a piece of code like this:

// other people's implementation
Obj obj;
stringstream ss;
ofstream outfile("save.pth");
ss.write((char*)obj.data(), obj.size());
outfile << ss.rdbuf();

I think directly write to ofstream would be faster, like this:

// my approach
Obj obj;
ofstream outfile("save.pth");
outfile.write((char*obj).data(), obj.size());

Why some people would like to use stringstream to pass the data?