If you really need it for cab book or any other details then buy from from outside airport or local market .
In airport around 95 UAE Dirham cost (More than 1500rs ) of DU sim for you and in local market its around 60 Dirham. And if you have postpaid sim then you can activate the International Plans for it.
You'll need to check what do you need it for. If you will need to make extensive calls, go for a local sim. Whatsapp call is banned irrespective of the sim card. However you can download a VPN app and make calls via whatsapp using wifi from your hotel. For internet plans you can check out Vodafone and Airtel which have good IR plans.
I don't think so that you must to purchase any sim there. I visited Dubai and had no sim card for that origin. if you're an Airtel or Vodafone user, you can be hustle free.
Yes buying a local sim is always helpful but always get it from the local stores and not the airport if want to save pennies.
Hope it helps, Happy Travelling :)
Thanks to all friends who have cared to reply to my query. I have opted for a 30 days Airtel plan that is available for Rs. 296/-. It offers 40 minutes worth of international incoming and outgoing calls to and from India. As for cellular data, I will rely on free wifi available in my hotel and elsewhere. Thanks again.