Windows service does not require any active logon to the server and it can be configured to keep running in background. Once this service detects any file creation, it can kick start the package. Also the execution schedule and logic to trigger the package can be made configurable by making the windows service to read parameters from a config file or from database.
I do not intend to say that there is no good use of File Watcher Task, but in cases of scenarios like the one I mentioned above, especially in mission critical production environments, if I were to make a decision, I would use the technique I suggested. It would be nice if Microsoft comes out with a nice scheduler level support for such requirements.