I often get asked why a student should take grades. The honest and best answer I can come up with having been asked this a lot, is ...."Because they want to take them."
If the idea of an exam isn't for you, then don't take a grade. You can still learn all the material, just don't take the exam, simple.
The syllabuses are well designed and thought out. There is graduated increments of learning that suit most players.
If you'd like a verification and confirmation of your abilities there is no more accurate measure.
For those wanting to enter Higher Education there is also an added advantage in that they do accrue UCAS points.
Below is a visual representation of the academic qualifications in this country and I will point out where the grades sit along side it.
Level 1 : Grades 1,2,3
Level 2 : Grades 4 , 5
Level 3 : Grades 6, 7, 8
Level 4 : Dip LCM
Level 5 : ALCM
Level 6 : LLCM
Level 7 : FLCM
Level 3 is where UCAS points start to kick in. So it is worth it if you are looking to bolster your points for Uni entry.
Example Grade 8 distinction is worth 30 UCAS points. So roughly equivalent to another A Level at Grade C.
I hope this clears up the Grade rationale.