As understand it, an Instant is either a slow cooker or a slow cooker/pressure cooker combination. If that's the case, it's the exact opposite of a skillet.
An IP in either mode is meant to cook foods, usually in a liquid, for longer periods to enhance flavors and tenderize tough cuts of meat. Think soups and stews.
A skillet is intended more for high heat/fast cooking applications like cooking a steak, bacon, chops, chicken breasts etc.
If my initial statement is incorrect, please ignore the remainder of the post (except this last sentence.)