Buying subsale is less riskier as you know the surroundings, the workmanship, the management, the developer, the rental market (whether it is rentable), quality of residents, the design and facade of the building.
Buying something from the primary market, more often we only look at the brochure You don't even get a brochure during pre-launch), the layout, the price and compared to the surrounding development. We are taking risk as we are buying much higher price which developer has included the higher cost of material, labor, logistics, transport & etc. We also taking risk on they quality of the building they going to deliver, the management team and so on. I am not saying buying new launch is not good. There are plenty of good projects too. I buy new launch too! Haha But i am saying it as a general.