The opposite is true - directory traversals themselves are effectively free, this is not going to be something that slows down your app - but loading the JS & c

The opposite is true - directory traversals themselves are effectively free, this is not going to be something that slows down your app - but loading the JS & creating the IR will be much slower. The 4 second startup time with npm2 & babel6 is almost certainly due to the duplicated dependencies, which means literally hundreds of megs of JS have to be parsed & warmed up. With npm3, the same files are (correctly) reused which significantly speeds up start time.