Sequential sampling is a non-probability sampling technique wherein the researcher picks a single or a group of subjects in a given time interval, conducts his study, analyzes the results then picks another group of subjects if needed and so on.
This sampling technique gives the researcher limitless chances of fine tuning his research methods and gaining a vital insight into the study that he is currently pursuing.
If we are to consider all the other sampling techniques in research, we will all come to a conclusion that the experiment and the data analysis will either boil down to accepting the null hypothesis or disproving the null hypothesis while accepting the alternative hypothesis.
In sequential sampling technique, there exists another step, a third option. The researcher can accept the null hypothesis, accept his alternative hypothesis, or select another pool of subjects and conduct the experiment once again. This entails that the researcher can obtain limitless number of subjects before finally making a decision whether to accept his null or alternative hypothesis.