Then I just start the watch task and change/save a display template:
Whenever I save an HTML file of my display template, it gets uploaded and checked-in in the Master Page Gallery. That causes a corresponding JS file to get generated automatically so I don't have to worry about managing it.
If you are maintaining your Display Template JS files in source control, you will have to remember to copy the generated JS file back into your solution.
Hope this helps you speed up your Display Template development. I have uploaded this project on GitHub here: https://github.com/vman/Gulp.DisplayTemplates
Thanks for reading!