For Non-Resident Indians (NRI), only the income that is received or accrued in India is taxable.
NRI should file Return of Income if his tax deducted at source (TDS @10.3% to 30.9%) is more than his actual tax liability. He is entitled to claim refund of Tax with interest.
Sometimes, NRI may incur short-term or long term capital loss on sale of investments. He can setoff such loss against long term capital gain from sale of investments in subsequent year or years provided he has filed Return of Income within the prescribed time for the year in which he has incurred loss. Hence the NRI should file the return of Income declaring loss in such a situation.