Of the 950 books I had, four wound up graded and slabbed. The AF15 was just bagged for close to fifty years. When it was still not slabbed, a very small chip popped off on a corner while I was putting it back in the bag. I don't think it would have changed the grade it finally got but it would not have happened if it was slabbed. Of the 950 books, probably 25 of them had a value higher that 2K. In retrospect, I would still not have slabbed all but three since I sold to a private dealer, not on Ebay. All three I did slab got 9.0 and higher and were forty plus years old.
If you are slabbing to protect the comic, I can see it since humidity, handling and sunlight both can damage the things. If you're planning to sell, I can see it since it established graded value. Beyond that, now you can't read them.