In my vast experience within the realm of credit - and personally debt, lots of debt - I've found that instant approval credit cards are pleasant to acquire. It's similar to going to a job interview and being told by the receptionist that you can have the job.
Now this may be because of over a decade of baseball I've played (the decade where you learn how to play, not the decade of being able to do it as a job), but the comparison that arose in my mind, the first time I received an instant approval card, was that of a pitcher throwing the ball over the centerfield fence for you, without you ever lifting the bat from your shoulder.
Maybe that's a stretch, but you get the idea. It's nice. All the stress and strain and worrying that comes with the approval process normally is not present. Just a straightforward 'yes, absolutely, you can have some credit.'
I should mention, though, that there is usually a down side to a good thing, and instant approval credit cards are no exception. If your credit is not up to the issuer's tastes, you will be met with an equally quick 'no.' This can feel like being pegged by that same pitcher while you sit in the dugout putting on batting gloves or eating a sunflower seed.
I will say, though, having been through rejections and approvals of many degrees, that an instant 'nope' is better than a 'no way you're getting one of these' response that you waited weeks to hear, which is a fate one can encounter with other cards.
Now there is one mistake that ought to be avoided with instant approval credit cards. When you get one, it does not mean instant credit, much to my dismay. It takes usually a business week or two for your card to actually arrive in the mail.
I discovered this the hard way. I received my instant approval online while I was shopping around the Internet for old rock and roll paraphernalia. My heart was nearly broken when I could not immediately purchase a frayed and slightly burnt guitar strap that once belonged to the rhythm guitar player for a band that opened for Credence Clearwater Revival. What? What? Don't look at me like that. You've probably purchased weirder things online than that, come on.
Anyway, that was how I learned that instant approval doesn't mean instant license to spend, which ought to be kept in mind for those of you about to get a card. Also, remember that instant approval does not mean a definite yes, it means an instant thumb-up or thumb-down. But you have to admit, the prospect of knowing in seconds what you normally wait days or weeks to know is an attractive possibility.