Does it makes sense to call sync() on output-only fstream?

I found some legacy company code that was using an std::fstream and calling fs.flush() after each write, then fs.sync() each time a certain amount of data were written to the stream. This code only needs to do output operations, not input ones.

std::fstream fs(filename, ios::out | ios::binary);
fs.write(buff, size);
fs.flush();
if (/* needs to sync */) {
  fs.sync();
}

This is surprising me as I usually use std::ofstream for output-only IO operations and because this class actually does not have the sync() method.

Since std::ofstream does not have the sync() method, does it makes sense to use std::fstream and sync() for output-only IO operations?

In my specific case, should I keep using std::ofstream and call flush without thinking about sync?