Assuming Geneva College, which offers meal plans of this description, which all cost the same price. There are some other plans that cost $190 less per semester.
21 meals per week is at least 315 meals at Alexander Hall or the Brig, since there are 15 weeks of instruction in a semester (and there should be more to cover final exam week, etc.).
So the 220 meal block plan is far fewer meals (probably averages 14 or slightly fewer meals per week). Based on the college’s web site, it looks like the student gives up the meals in exchange for being able to each a second meal at the other dining hall during the same meal period, and bring guests in for meals.
The 180 meal block plan’s 150 flex purchase points can be used at additional places besides the two dining halls. It looks like flex purchase points roll over from fall to spring semester, but expire after spring semester.
http://www.geneva.edu/residence-life/housing/res_mealplans
http://www.geneva.edu/admissions/forms/forms_21meals
http://www.geneva.edu/admissions/forms/forms_220block
http://www.geneva.edu/admissions/forms/forms_180meals_150flex
It looks from the campus map that the campus is not that big, and the Alexander Hall dining hall is closer to the academic buildings than the dorms, so that access to meals between classes is not really an issue.
http://www.geneva.edu/about-geneva/campus_map
However, the 220 meal block plan and 180 meal block plan plus 150 flex purchase points cost the same as the 21 meal plan, and some other plans cost only $190 less per semester. It does not look like there is much savings to go for the fewer meal plans, unless the student plans to bring guests.
It is rather likely that the cost difference is small because most students taking the 21 meal plan do not use all 21 meals per week, although they may use more than 14 meals per week.