Like many experienced collectors I am confident in my ability to tell an authentic piece from a reissue, custom, fake or reseal :!: Therefore that isn't the no 1 reason I choose to get some pieces in my collection graded.
Yes UKG/AFA make mistakes but as a percentage of total work done it is v minor :!:
Pro's;
When it comes to selling/buying online these grading companies can really help in increasing trust in pieces in question.
Grading MISB can preserve a period in time ie even if the tape pops because it is entombed one knows it has never been opened 8)
Being entombed protects the piece v well and it is documented.
Con's;
As said once entombed one cannot touch, smell or explore the piece anymore :!: I think this is particularly highlighted when we r talking about 'Q' grading :!: I think one has really lost out no longer being able to look inside an already opened piece to c the beautiful uncorrupted factory contents :!:
Having a piece with considerable flaws graded just highlights the damage and or decay on the piece via the low grade awarded :!:
I personally decided to preserve the sealed boxed pieces in my collection and get a couple of my iconic and top condition MOCs graded, documented and naturally well protected.
As said there is no right and wrong, just personal choice