Why gypsum plaster is used against conventional plaster method of cement and sand?

Because gypsum plaster has extra advantages compared to cement-sand based plaster as indicated to save time working, free cracks, leveled smooth finish and  energy saving due to low value of thermal conductivity.

Gypsum plaster is easy to use, and ecofriendly, water saving also

water resistance, fire resistance,  free from cracking,  

Could you Explain more about Question ..Kindly .

gypsum plaster is fast becoming the preferred option to plaster internal ceilings and walls. It is ready to use, requires no water curing and is labour-friendly,eco-friendly  and faster than sand cement plastering. It also delivers a crack-free and smooth finish.

gypsum plaster finish is not the best, there are much better products to the plaster finish that is used to save money but suffers moisture. mixing sand and cement plaster is called and it is not a finished wall, in Italy it is smoothing stucco after the plaster