If your trip is 14 days long but you only move between cities twice, buying individual "point-to-point" tickets is significantly cheaper.
The fastest bullet trains require an extra "supplemental" fee even with the pass; individual tickets let you book these directly. Pro-Tips for Timing when to buy jr pass
You plan to use the Shinkansen (Bullet Train) multiple times a day for spontaneous side trips. If your trip is 14 days long but
If you are only exploring one area (like just Kyushu or just Hokkaido), a Regional JR Pass is much cheaper and more effective. when to buy jr pass
If you are mostly staying in Tokyo or Osaka and doing local day trips, the pass is a waste of money.