You get drag-and-drop, card previews, sorting by custom categories, and price data from TCGPlayer, Card Kingdom, Cardmarket, and Cardhoarder
Rares are where you start seeing more powerful build-arounds, board wipes, pushed creatures, unusual enchantments, premium lands, and cards with effects that would be miserable if they appeared too often in Limited
In particular, what (vocal) Explorer players want are the 30-ish or so cards that would make pretty much all top-tier Pioneer decks playable on Arena
I'm down to smack people with trees and rocks
Sleeves that are too tight can damage the cards, while those that are too loose may not provide adequate protection