As I found out, having moved from one to another country, the country where the credit card is issued in will determine which country's iTunes store you can buy apps or movies or books from.
If you switched stores, you need a valid billing address and credit card from the country you're switching to. You won't be able to download apps, movies or books if they are not available in the new country's store.
For example, there will be apps only available in the India app store but not in the US store and vice versa. You would need to download them first before switching to ensure you'll be able to keep using them.
Before switching country /region in iTunes, you will need to cancel any active iTunes Match subscription. You can switch stores back as long as you have a valid billing address and credit card, and then you will be able to have access again to your purchased apps, movies or books. All other purchases are not transferable.