The babel performance stuff is pretty bad, even when using a watcher. I was building another project on my netbook (admittedly a slow computer) and it took 10 seconds (!) to compile a single 400 line es6 file. There's so many people using it now I'd be shocked if it wasn't improved rather quickly, but still it's pretty wild that it got launched like that. (On my desktop it takes about 1.5 seconds for the same file, for comparison)