[dagw]

The JR pass really is a nobrainer though.

I really recommend doing the math based on your particular itinerary. I've been to Japan twice, 14 days each time, and, at best, I would have broken even on a JR rail pass based on the traveling did. For longer trips, like Tokyo <-> Sapporo airplanes are both quicker and cheaper.

[paraselene_]

It's more for flexiblilty and peace of mind, with a all-you-can-ride ticket, you can book all itinerary/reserved-seat tickets(when available) right when you land, and have the flexibility to bail on any single train connection when you couldn't make it, either because of emergencies, or you just like the place you're visiting so much that you'd like to move your tour schedule around a bit.

And it's not like you have to get the pass for all region, there are dozens of types of regional jr passes depending on the region you're visiting. Those are the ones that's of better value when travelling in-region, and covers most touristy places. Personally I'd say tokyo-wide, kaisai, and hokkaido are the ones that's pretty no-brainer when in those regions.