In 2013, the U.S. stock market soared. The Dow was up 26%, S&P 500 gained more than 29%, and the Nasdaq surged nearly 40%. This feat was not repeated the next year, though the market rose. In 2014, the Dow was up 7.5%, the S&P 500 11.4%, and Nasdaq 13.4%.
Hence it does make sense to invest in another market.
The Indian market is not always on a roll. In 2011 when the domestic stock market was battered, a marginal exposure to another geography would have helped curb the hit a portfolio would have taken.
But consider a global fund only if your portfolio is well diversified domestically and your core holdings are in place.