Perhaps the biggest short term significance of the Musk home batteries which will store power generated by solar pv arrays (or wind turbines) is that they will help grassroots renewable energy generators fight back against monopolistic utilities in countries such as the USA and Australia. Various of these dinosaurs are trying to strangle the decentralised energy revolution at birth by refusing to pay much for solar pv 'exported' to their systems, or, even worse, in some cases, by actually charging the home generators for the privilege of using their electricity wires.
Hence these batteries will be of good practical use in helping the renewable generators fight back. They will be able to store their production when it is generated and use it when it is not sunny, or windy. They won't need the dirty power from the wires owned by the utilities!
In Germany there are already said to be 18000 homes which use batteries to go 'off grid'. See http://www.nytimes.com/2015/05/14/business/international/with-tesla-entering-market-hopes-for-home-batteries-grow.html?smid=tw-share&_r=0
If the utilities were more enlightened and had any foresight (unlikely in many cases) they would encourage local renewable generators to utilise storage systems in order to avoid spending money on grid upgrades and power stations. But don't expect the bog boys to rush at this one....
But for Elon Musk, it's (also) a damn good advert for his electric cars!
If you haven't noticed the news articles already (difficult) see http://www.wired.com/2015/05/tesla-batteries/