Supervising same work again and again I found few professors having supervised more than 200 masters theses 'each' in the past 14-15 years. When looked at these theses, I found that out of 200 theses supervised by a professor, more than 100 works were based on the same idea:

theory is same
method of analysis is same
results and discussion are alike (similar)
proposed future works are same

Only the data sets are different, that is in thesis 'x', he used data in the range 1-2, in thesis 'y', he used data in the range 2-3 and so on. In some cases, I found that even the data set in a particular range, say, 1-2, collected by different filters/methods were distributed to 5-6 students and asked to do the same same work. Even after 14-15 years, the future works to be done have not changed. The proposed future works are appearing same from one thesis to another. I noticed the same behavior in the remaining theses also. The whole bunch of theses were just based on 2-3 ideas.
So, the question is: if such type of works repeatedly supervised is good or bad. My personal feeling is that it is a bad practice. Even in masters thesis there should be newness.
This is a poor supervisory practice. Unfortunately, it becomes increasingly common in Universities, particularly in countries with strong marketalization of Higher Education (e.g. US, UK). Students are treated as customers, and academics are assessed and promoted based on their &quot;efficiency&quot; in terms of the number of students they supervise, not the quality of education they provide. The pressure on academics to supervise more students is constantly increasing, and they rarely have enough time to meaningfully prepare to supervisory meetings. It is not surprising that many academics find it convenient to reuse the same projects over and over again.
UPD: Answering comments, I want to clarify why this practice is detrimental to students' learning. Project-based learning attempts to recreate an authentic experience of doing something, then encourages students to reflect on this experience and learn from it. The authenticity of experience is the key for success. However, after some repetitions the supervisor knows all good and bad ways around the project, and unconsciously projects them to the student. Students don't have the same feeling of terra incognita in their research. Of course, realistically, we can't expect each master project to be completely new, but it's still important that the supervisor has not rehearsed it by heart yet.
A closely related, but not exactly the same reason is potential plagiarism. All theses are published and could be dug out by students. I have seen some supervisors who passed good theses from past years to new students to &quot;get the style&quot;, effectively encouraging plagiarism. But they had way to many students to supervise and no time to do it properly. Surely, copying from someone else's paper is a poorer learning experience for students compared to doing research themselves.