The watch node may fire multiple times during the writing of a file. This means that it is often (very often in my experience) necessary to follow the watch node with a Trigger to delay the message till the write has finished.
The underlying library (which I believe is chokidar) has an option awaitWriteFinish which is documented as delaying the watch event until a little time after the file stops being written to. It would be useful if the Watch node had an option to enable that in order to avoid the requirement for a Trigger node.
This problem is regularly encountered on the forum, see Using a watch node for example.
Correction: The watch node does not use chokidar, it uses fs.notify