Arkham Horror is a very expensive game if you buy all the expansions. If you choose to sleeve, you can only do that using FFG official sleeves for a snug fit (don't know if there is a cheaper alternative besides not sleeving at all). The Sheet Protectors are for Ancient Ones, Investigators, Guardians, Heralds, and anything else that will not fit with sleeves. For those interested in how much it has costed me to sleeve everything before tax (and rounding a penny up, where needed)…
Fantasy Flight Supply (Green Package) 50 Clear Sleeves 57x89mm. = $3.00x30 = $90.00
Fantasy Flight Supply (Yellow Package) 50 Clear Sleeves 41x63mm. = $2.50x20 = $50.00
Protect&Store 8.5x5.5 1" Binder. = $7.50x2 = $15.00
Sheet Protectors 15 Pack. = $6.50x7 = $45.50
Ignoring the binders, this does not include storage, which I have been wondering if there isn't a better solution to that. Been using Deck-Box Ultra Pro cases ($2 a pop) but they do not hold very many of the 57x89mm sleeves well; however, they work well with the 41x63 sleeves. Also using an Angled Storage System by Plano (got for about $40, which previously held Descen tokens, figurines, and tiles).
If you choose to sleeve and store, just wanted to warn you of the nearly $300 dollars of storage you may acquire if you want your AH in order.