Personally I much prefer to use code that's already written+tested like lodash and moment, rather than write it myself. I feel like when you've already got apps like Sticky Notes and Box Integration and other stuff really bogging down load times, then agonizing over a few kB of file size for a useful library is counter-productive. Users aren't going to notice either way. Different issue on an SCA website or something, but when I'm working within NetSuite, file size is the last thing I worry about.