Granted, something like CGC would probably be 
better for cels or cards, because you don't need 
to crack the damn shell open to appreciate them. 

(Although I'm not really in favour of encasing 
anything permantely in plastic, unless it's 
mylar. I have non-mylar archival grade bags which 
have turned cloudy over the years, and it's hard 
to appreciate anything I have stored in them. 
Anyway, according to a professional archivist, 
you can expect plastic to last on average 50 
years before it becomes brittle.) 

As for cracking a CGC with a comic book in it, 
the value on the sheet becomes void, because it 
can't be guaranteed.