In the hangout with John Mueller and Martin Splitt of Google, Martin Splitt said “the two waves of indexing play less and less of a role.” He added, “I wouldn’t say that two waves of indexing are dead, it’s definitely not. I expect eventually rendering crawling and indexing will come closer together.”

He also added that a lot more than you think goes through the render phase because it is super cheap. We thought it would be expensive for Google to send pages through this render phase, but this was wrong and turns out to be very cheap – so cheap they send non-JavaScript pages through it anyway.

This is all in the video starting at 32:03 into the video. Here is the video followed by the transcript:

I am not sure if this fully explains everything but it does shed more light on this process.

Forum discussion at YouTube Community.