Slabbing in practice has it's purpose for certain type books. Rare issues, major 1st appearances or major continuity shifts perhaps. As noted an Action #1 or even going more "recent" say a Tomb of Dracula #10(first Blade).
Slabbing a Blackest Night #5 then asking $100 for it is flat out wrong. The book is not worth that. You have to pay a fee to have it slabbed and peoples asking price is rolled into that.
These CGC people managed to take an existing indusrty staple of grading, the Overstreet Guide, with Mint, NearMint, Fine, Good and Poor and declare themselves the "experts" on what is considered Near Mint or Fine. To do this Each category was now numerically coded but their decision was final and the industry and collectors ate it up.
It totally took away from objectivity.
I'd been to shows where some guy said Near Mint and it clearly wasn't. But you could discuss, haggle and either come to an agreement or not. With slabbing everyone is now, "Oh, it's a 9.5" end of discussion. Bullshit.
I have seen a graded 8 and a 9.5 beside each other and can't see a difference. It's a sucessful scam that all seem complacent to imo.