But even then it's still good to be connected to the grid. It will serve as a backup line and if you produce more enery than you can consume, you might be able to sell something back to the grid.
Once the question is framed properly -- at least for a few million people in the US -- then the motivation for storage becomes much clearer. If you have a battery and an inverter then you hook that up and it feeds the house. And all your other power generation choices feed the battery. Solar, wind, hydro (if you live on/near a stream or river), small generator, etc.
If it costs $100k to get hooked up and then you're paying some fee for power every month it might make sense to buy the battery for $20k, buy a generator for $5k and spend $10k on a wind turbine and $10k on solar. That's $45k versus $100k which is a good chunk of change plus you can expect your prices to go down as solar panels and batteries and whatnot get cheaper, whereas fuel is only going to get more expensive.
Maybe I'm just spoiled by the German power grid. As far as I can remember I only a single blackout of 30 minutes in the last 15 years (some time around 2008).