What benefits exactly we get from using gas in the network and why do we need it?
Gas is used as an ETH independent unit of accounting.
It let's you define how much a certain operation in the EVM (Ethereum Virtual Machine) should cost in relation to each other. In this sense it is a cost structure.
The benefit is to decouple the incentive structure for cheap opcodes from a certain price. If the value of ETH increases, miners can choose to lower their demand for fees in ether smoothly. So with this, a mining fee market can always adapt to ETH valuation.
Ethereum is essentially a single Quasi Turing-complete computer, capable of computation just like any other computer, except for every instruction executed, there must be something expendable known as gas. Gas is essentially a limited resource required to run computation to ensure that every contract will halt/terminate and did not cause Denial of Service.
tl;dr Ethereum Developers' solution for halting problem.