Short answer: it depends. You have probably seen people fish with and without a net and wonder why. If your fishing line and rod can support the weight of the fish, you can simply lift the fish onto the bank or deck of the boat.
Benefits of using a fishing net:
Some people choose not to use a net. Usually, they don't want to carry another piece of gear or feel it needlessly complicates landing the fish. Without a net, you will typically use a free hand to grab the fish. For large fish, some people will even get in the water with the fish to land or release it.
Fishing Fundamentals