It's not a completely original move -- Netflix has done the same with other shows in India and South America, while Apple TV+ made a bunch of episodes available for free when it first launched. Obviously the idea is to hook people onto a series and encourage them to sign up for the whole shebang. In the case of The Crown specifically, though, the deal is likely to appeal to older folks who rely on the BBC or ITV for their TV dramas, and could help coax them away from regular television.
The free episode launches on November 17th -- the same time as the rest of the series, which this time around features the likes of Olivia Colman and Helena Bonham Carter. It'll be available on a dedicated site, netflix.com/thecrown, until December 15th.