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I'm old-school enough to remember when devices were held together with screws -- or even nuts and bolts! But Apple doesn't like fasteners because they ruin the lines of products, and make it far too easy to get inside a device.
With that in mind, a great many of Apple's current product lineup -- including the iPhone 5, iPad 4, and iPad mini -- make extensive use of adhesive to hold components in place. Adhesive is used enthusiastically to hold in place screens, batteries, cabling, and even components.
Using adhesive to hold in place consumables such as batteries makes repairs tricky, Prying the battery free from the adhesive can damage components, and even puncture the battery.
Image source: iFixit.