Sampling is more suitable when we have short time?

It depends on what you're dealing with. Sometimes, gathering the whole population is not possible.

 

Scenario1: if you have to collect information about US company profit margins in2013, it's not possible to collect such information about every company as many are privately held and don't share their financial statements. So in that case, you would collect a representative sample.

 

Scenario2: On the other hand, if you have to collect information about all currently enrolled  students in a particular school, then such information would be available with the school authorities. In this case, yes, you would collect a sample if you were short on time. 

Hi Mehwish, Good morning. In my opinion, sampling will be beneficial in case of shortage of time. But, usually it all depends on many factors. Priority wise.1. Cost.2. Time.3. Population for the study if it is large then sample is used to derived prediction about characteristics.4. Available Resources. Prudently drawn sampling always beneficial.