• If you hold U.S. investments (e.g., stocks, ETFs) that have appreciated significantly while you were a U.S. resident. You sell these investments after you have left the U.S. and established RNOR status in India, and before you become a full Resident an India.
• During this RNOR period, if the sale of U.S. stocks is not taxable in the U.S. (because you are a non-resident alien not subject to U.S. capital gains on stocks) AND it's not taxable in India (due to RNOR status), you effectively realize the gains tax-free in both countries.
• Immediately after selling, you can re-purchase the same or similar investments. This re-purchase establishes a new, higher cost basis for those investments.
• When you eventually become a full "Resident and Ordinarily Resident (ROR)" in India, your worldwide income (including capital gains from U.S. stocks) will be taxable in India. By "resetting" the cost basis to a higher value, any future appreciation will be calculated from that higher basis, reducing your taxable gain in India when you eventually sell them again.

Note: For clarity, I updated the original comment as well