For the jobs at the earlier stage, Mr. Fang didn't have to play the offline mode. However, the Fleeca Bank Job was more like a tutorial job and was quite easy. In the following jobs, the players needed to operate all kinds of tools, including piloting planes and helicopters frequently on top of cars, and he had to master all kinds of skills.
So, even Mr. Fang had to go to the offline mode to obtain the knowledge and skills.
For example, in the Prison Break and the Humane Lab Raid, the players had to fly the Hydra VTOL Jet and the Valkyrie Helicopter, which required the players to be able to drive or all kinds of machines on the road or in the air.
By now, Mr. Fang could only drive cars, and he needed practice before he could operate other machines.
Of course, there were other ways to make money in the online mode. If they were interested, they could even speculate in the stock market, purchase properties, and hold illegal racing competitions, etc.