Google is implementing a pretty simple and seemingly obvious change: font-dependent line spacing. This is something that Microsoft Word and other word processors already do, so Docs documents will now be closer in length to documents from non-Google programs.
Looking at the chart above with three 10-point fonts, it's clear that Times New Roman has the smallest spacing with Docs' new formatting. Comics Sans makes it slightly bigger, and Sue Ellen Francisco has the largest spacing by far. Google says that this will not only make documents written in Docs and those written with other processors more consistent, but also help ensure that converted Word documents stay at a similar length. For students who have to meet certain requirements on how long their papers have to be, this could be useful.
This change is rolling out today, with full rollout scheduled to be completed within one to three days. It'll be on by default for new documents, but existing documents will be unaffected.