There are indeed many advantages to such an opening, both for the region and the Parisian institution. It will bring art to people usually not accustomed to visiting art institutions. In a TV coverage, some visitors said they hadn't gone to a museum in years. It is also expected to attract tourists to a rather uninteresting part of France, unless you want to know about the mining past of the country or are commemorating World War I brutal events (there are many military cemetaries where mostly British soldiers are laid to rest, and that alone is heart-wrenching).
There are many advantages for the Parisian museum as well: many art works usually stored and invisible to the public will now be available. And for once, visiting the Louvre will not be the excruciatingly tiring experience it is in Paris (been there only once, it took me only 45 minutes queuing to get in (which is very fast), and the crowd was so packed around the Mona Lisa and Venus de Milo that I actually didn't see them).
It is not the first time a highly acclaimed art institution opens another museum or wing in a far location. The Guggenheim Museum in Bilbao comes to mind, and everyone in Lens hopes it will the same effect this opening had on the Basque city (it will be interesting to see if the Cultural Capital in Marseille will have the same effect it had in Lille, another Northern city, although less economically crippled than Lens).
It is hoped the Louvre-Lens will attract foreign tourists. Time will tell if it was a winning move. So far, the first tv coverage has shown Polish tourists, but they were in the region because they were visiting families (there are many families of Polish descent in this area, due to the immigration waves at the beginning of XXth century).
Some have criticized the Louvre move, saying it will tarnish the magic aura of the Parisian institution. A small price to pay for bringing art to a region with few artistic venues.