Worker mode runs exactly the same code, but in a different thread. So it probably won't be running the same code any faster, but it has better performance characteristics, as anything that blocks the main thread can jank the game in DOM mode, but can continue running smoothly in worker mode. In a standalone app like NW.js there should not be much that affects the main thread, it's more useful for stuff running in browsers where there is more likely to be main thread contention.
As ever, if you want to know the real answer about a performance question, measure it yourself. If you can't see that it makes a difference, it probably doesn't matter.