Hi Gerard,
Good question. lolol. And good point, you did ask about 'how it helps' and I didn't directly answer that, so here it is.
Schema.org provides a set of guidelines for publishing structured data on the web in various formats. You can read more detail on our website.
The answer Part 1 : Schema.org helps publishers, small and large, even folks like you and me that might have small websites with important data, that can be crawled by bots, public scraping scripts, etc. to harvest more public data for Wikidata to absorb, as well as helping to reconcile data and even load the Primary Sources tool, Reasonator, or any tool eventually if we wanted. Adding references could in theory just be done by a bot that was smart enough to understand Schema.org markup (there are already many Python, Ruby, Java libraries that exist for this).
The answer Part 2: By having Schema.org properties and classes aligned to existing Wikidata properties and classes. Both sides benefit to help understand that structured data even more....and once a machine understands it better, than those machines can be programmed to gather even more data, or validate the quality of the existing data.
This mapping effort is not just limited to Schema.org however in the long term. Notice that we already have many mappings in Wikidata for external vocabularies, but its very rudimentary. We want to help Wikidata have a more full understanding of data, and that requires a few more properties to be added to support that effort.
Lydia understands this. In fact, she was one of the motivators to have us encourage us to perform the mapping on both sides, inside Wikidata and inside Schema.org (both will be done, but first it was deemed necessary for Wikidata). In addition, she understands the struggle to bring in more quality data for Wikidata and to help tool authors and publishers, which in doing so helps with Goal 1b of WMDE's future plans. Lydia and a few of us from Schema.org will be having a Google Hangout to discuss a few more details this Friday. The entire effort and comments are being tracked here: https://github.com/schemaorg/schemaorg/issues/280
Thad +ThadGuidry https://www.google.com/+ThadGuidry