The speed of getting data into memory without having it stored locally, or needing an external server process for that purpose! It's not perfect yet but I think they're working towards making this happen with their new version (1).
But at least so far you can use ala sql as your own local db using node js/browser javascript only if thats what u need right now :) We are solving our problems by storing large amounts of customer information from various sources online such as social networks etc.. This helps us keep track of who we want to contact next when there isn't any other way available like emailing them directly which could take days sometimes before someone responds back due to heavy workloads elsewhere within companies where these tasks fall under responsibility. So instead its quicker just store all relevant info about customers here first then go through each one individually later once more staff have time again rather than waiting weeks until people get around.