Anime-Beta TNG

I have recalled recently seeing somewhere that when storing cels, it is best to skip at least 3 pages every time you place a new cel in the binder. Is this true? It seems a little much, imo and I would like some sort of explanation if possible.

I never heard that and don't do that either with any of my Itoya's
The main thing I have found is to store them on edge like files in a file cabinet and not store them flat where the cels can be damaged by weight.

My policy for storing cels in an itoya is only 1 cel per sleeve. So I skip 1 page (not sleeve). Usually itoya you can do 2 cels per sleeve because it's two pages. But I find that even with the black insert, there's still a co-mingling of gasses for the acetate that makes everything just caustic. You can try putting the sketch at the back but that just adds another plastic and another acidic item (sketch) in the sleeve.

Here's my setup per sleeve
1) 1 Cel usually not bagged (usually others will bag the cel before they put it in the sleeve but I find that unnecessary nowadays and I'm always afraid that the poly bag used might interact with the acetate anyway. Paper is less volatile. If you store your portfolio laying flat creating pressure and you are in a humid environment or never check your cels for a year - beware that your cel might stick to the black paper insert.
2) Black paper insert - i usually replace this after a year or two
3) Microchamber paper - behind the black insert. The black insert acts as a buffer between the cel paint and microchamber paper. I only have this to "capture" the gas the cel gives off. Also has to be replaced.

The obvious disadvantage to this is you only get to use 24 pages out of the 48... But the advantage i think is that you minimize deterioration and also since it's thinner, the portfolio doesn't buckle under the weight and I can store them on "edge" like JWR.

Hope that helps.