Disclosure: I worked at SolarCity from July 2010 until December 2014 and still hold and am long $SCTY (or $TSLA in the future)
Let me start by saying as a $SCTY shareholder I'm not thrilled about the price I'm getting ($25 or so) but ultimately I think it will be better for the world in the long run and I hope the Tesla-SolarCity merger goes through. I also don't think I could give as good of a bullish case on the merger as Jigar Shah just did.
It is the belief of most of the major decision makers involved that these ideas could be mutually beneficial when packaged together. That combined with (IMO) the deep discount SCTY can be bought for right now, the decision was better to make sooner rather than later. Elon has said that it's easier to create a single product and that's true, but David Crane's analysis that SC needs a reboot and couldn't survive this reboot in the public market is probably also true.
So let's look at an optimist's view on the combined final product:
I think I've read that SolarCity will take on the Tesla name, I only assume as the Tesla Energy (TE) brand. There should immediately be sales installations at Tesla stores in the states SC currently operates in, hopefully accompanied by an initial boost in leases/loans/sales in those areas as this is business as usual for SC/TE once the sale is made.
TE needs to stop with the pushy door to door tactics that made the leases popular and instead rely on referrals and word of mouth sales. Think of how many ads you saw Tesla run for their Model 3 launch that saw 400,000+ pre-orders (mine included)... oh wait, you didn't. We've already seen evidence that solar is contagious and SC's referral business has been a success. An emphasis on distributing the work needed to acquiring new customers to others (thoughts on that shared here) should drastically reduce the cost of marketing and sales overhead, a painful but necessary step to rein in costs.
SC as a company created a TON of jobs but some jobs inevitably become unnecessary when the organization becomes more efficient. SC's operations department has become a machine when they're stocked full of scheduled jobs but during seasonal down times they become another unnecessary cost. Their operations department is a huge success story in the field of construction management, the efficient gains they've made are remarkable but are getting harder to come by.
What I'd like to see TE do is the same thing they did with their sales & marketing streamlining and distribute the work of their operations department. You decentralize your installation work. You'd be bolstering the independent contractor installer network by distributing not only your workers but also your knowledge by creating an industry-wide standard of installation excellence. This will be hard for Elon and SC management to agree to as they like to have their finger on the quality from top to bottom and it may seem like you're losing that high standard of installation quality. However it is simply being transferred via your industry-leading training and certification program to locally-owned and operated installation companies.
Publicly it would look like TE is getting rid of A LOT of SC construction jobs and officially they are but overall those jobs are still being filled by the independent installers that are installing up to your standard (and even inspection) but are locally-owned and operated. So you're actually creating a lot of small business owners, something that is always well-received.
Behind the scenes, I'd expect the Tesla and SC HR departments to see which roles are now duplicated, which are necessary independently, and which are mutually beneficial. Then you decrease the positions that are duplicated and increase the mutually beneficial ones. I think these are the main synergies Elon and Co. talked about initially. I expect their battery and solar panel gigafactories to learn from each other and both benefit as well.
By distributing a lot of SC's work (both in creating the sale and installing the solar panels) they can streamline their costs and become more profitable. Elon's always been a huge proponent of economies of scale and I think you can still have this with a distributed sales and installation force by controlling the standards instead of the workforce. You'd lose a couple process efficiency points in the process but you gain that and more by not having to control everything.
I believe such changes can be beneficial to a combined company and I'm hopeful for the Tesla and SolarCity merger to finally go through, as it seems like it has been a long time coming.