I guess it depends on what you're doing. It never hurts to have an understanding about what's going on behind the scenes.
If you're purely doing 'look-and-feel' related frontend work likes design, css, accessibility, UX stuff like that it probably won't help you much in your daily work, but if you're also doing logic with JavaScript it'll be a great advantage for any moderately complex app, knowing at least some basics will help you make more maintainable and better performing code.