What are the disadvantages of the grading system, as opposed to the percentage system?

Grading suggests an 'absolute' judgement, good/bad, where Percentage-systems shows you your position on a spectrum, it's not just about good, or bad, it's more about you.

Percentages are one type of grading system. A grading system is any system by which a teacher assigns some indication of evaluation of your work- it can be A, B, C grades, percentages, points, a word such as "Satisfactory", "Unsatisfactory", etc.

Assuming that you're asking for a comparison of the A,B, C, D, F scale versus percentages, I actually prefer the letter grades. Most tests and other evaluations in classes have not been validated, so teachers can't really say that there's a difference between 87% in the class and 89%, for example. It's ridiculous to pretend that students can be assigned numbers that specific that really reflect what they've learned in a class. However, it's pretty easy to distinguish between those students who have mastered most of the class material and skills (A), those who have average mastery (C) and those who did master enough to move on (F).

Computerized grade sheets have pushed all of us into using numbers- usually the 100 point scale or percentages. But I don't like it.

All grading systems are used for two purposes: describe the amount a student has learned of a subject and how he/she ranks in the class. A high grade (A or B) may not accurately describe the amount a student has learned of the subject.

none grading is better