Tata Photon plus Offers 5GB free Data for Rs.5 only

Tata Photon data card price has recently been slashed from Rs.2500 to Rs.1799 and now TTSL has added some more benefit for prepaid customers. Postpaid customers were already eligible for 100% cash back but now in prepaid too customers get additional benefits.On purchase of Tata Photon plus prepaid data card for Rs.1799 customer can use FRC (First recharge coupon ) of  Rs.5 to get 5GB of free data for 30 days. Similarly FRC of Rs.2 gives 2GB of free data. But I wonder why would anyone go for Rs. 2 FRC and not for Rs.5 wherein only by paying Rs.3 more one gets 3GB more data.