Heya frankth,
I think that if you're going to smoke a bowl or two a day, and are going to go through the tin within a month of opening, you're probably good to go with leaving that 'baccy in the tin. If you're like me, and won't go through the tobacco that quickly, I think you're better off jarring them. I'm far from a purist though, and know there will be others of differing opinion.
If you're not going to get into the tins right away, and can keep yourself from popping the tin open to look at and smell your new tobacco, then they're good to hold in the tin until you're ready for 'em.
Enjoy!
-- Pat