Is it worthwhile writing about previous experience with courses, which will be taught in masters program, in motivation letter? I am applying for a masters program. I have read about the courses, which will be taught at the program. In fact, I think that I have had a lot of such courses in my bachelors program. Does it help to specifically mention that I think that I will do great at the program, because I have taken similar courses before? Also, I have got Bs for some of the courses (actually, the most of my classmates have done similar or worse, the grading was really harsh).
Anecdotally: I did this when I applied for CSE masters programs coming from a background in engineering. I highlighted the graduate level and elective courses I had taken in numerical methods, optimization etc. to demonstrate that I had interest in, and aptitude for, the courses on offer in the masters program. I also chose the professors from these courses for my references. 

I think it can be worthwhile to do this if it fits the narrative of your motivation letter as it shows that you have considered why you want to study these particular courses and why you would be a good fit for the program.