Skins and silicone protective wraps are great for protecting your iPad's finish from scratches and marks. But the mobile nature of the device means that you're at risk for dropping, bumping or crushing damage when going mobile.
Unless you're planning on just using your iPad in one location, a protective carrying bag is a wise investment. These bags are often smaller cousins of the protective laptop satchels and backpacks tech-savvy users have been carrying for years. But thanks to the iPad's small size, they can be much less obtrusive and more flexibly fit your style and carrying needs.
The biggest difference between these accessories and skins is that skins can stay in place while you use the iPad, while these protective accessories are for carrying, not protection during use. If you're truly concerned about protecting your iPad in all scenarios, consider buying both a protective skin and a protective carrying bag or case.