> Network data access costs a lot of money in some countries

Very much this. I live in a country which has country wide LTE coverage in populated areas. While the network is fast, data is very expensive. Here 1GB of data in a bundle is around 35 USD, where as back home I can get 25GB for the same.

I have mobile data turned off for most apps because of this. Everytime I open one (even if it works perfect offline) iOS pops up "Mobile data is turned off for XXX".