If you are not familiar with Amazon's Kindle Delivery Fees, you should check out their HELP Section on this topic, which can affect your book pricing and your subsequent royalties. As you'll see, if you select the 70% royalty option, a delivery fee of $0.15/mb will be charged, on each sale, before your royalty split with Amazon is calculated. As an example, if your deliverable file size (final mobi file size) is 10MB, Amazon charges you $1.50, deducted from your sale price, before they split the remainder with you, 70/30%. This is important to think about when you're creating your book, if you are using a lot of images, charts, and the like.
Remember Amazon's Royalty Calculation: Royalty Rate x (List Price - Delivery Costs) = Royalty
You don't want to inadvertently create a book that's 20mb in size, with a $2.99 sales price; you'd end up with the delivery fee costing $3.00! Obviously, that math won't work, so always keep it in mind, as you design your book. For books purchased in Mexico, the delivery fee is $1/MB--not $0.15, so if you are creating a Spanish-language book, this could really hurt you. (All figures in USD).
Important note: if you create a "coffee table book," you may decide instead to opt for the 35% royalty option, which incurs no delivery fee. Some of our artwork-book clients have chosen this route pretty successfully. It's a viable alternative, if you know that your book needs a lot of imagery to work.