In a perfect scenario, you'd be able to analyze information on every single individual in a target population. Many of us, though, do not even have the budget or resources to acquire this data. That might have been possible if your target population is small enough — for example, all the people of a small town or all of the students of a particular college.
That is why survey sampling is important. It allows collecting data on a sample of your target group. “Representative” is the important word here. You must carefully pick your sample in order for a survey to accurately reflect the target audience. It must be suited to your targeted population's demography which can be too huge or small.