I use a DSLR (I'm a Nikon shooter) for my regular photography jobs and assignments. I also take it with me when I travel but I was a bit tired of carrying it around on my travels, especially that it's quite heavy (the battery grip adds lots of weight to it) and I wanted to have an all-in carry-around small point-and-shoot. I decided to buy Canon S100 but, for some reason, I was postponing buying it. Then, just a couple months ago, I bought a second-hand iPhone 4s and everything has changed.
I was really surprised how quickly my new iPhone has become my point-and-shoot camera. I was every more astonished how it has become my main camera during my travels.
Quality - I think that the quality of the pictures for a phone camera is great. Although many (if not all) point-and-shoot cameras on the market have much more than 8 megapixels (that what iPhone 4s has), it's not about the pixels here.
Panoramas - Shooting a panorama is a new function built-in to the iPhone's camera software (I think panoramas were introduced in iOS 6). You just slide the phone from left to right and the software automatically stitches the picture together. It works really great!
Geotagging/GPS - That's my favourite feature when I travel and when I take pictures of potential future photo shoot locations.
Sharing - And of course I can instantly share the pictures on social networks or other websites.
It's always with me - I think it's self-explanatory. I always have my phone with me and so is my phone camera now. I don't have to worry to remember to take my point-and-shoot with me, because the phone is always in my pocket.
No RAW - that's quite obvious, iPhone doesn't allow you to shoot in RAW. I thought I would miss this feature but so far, I don't. I haven't had a need (or desire) to post-process pictures taken with an iPhone on my computer. I just use the phone for mobile photography, I edit pictures on my iPhone (or iPad) and that's it.
No Controls - Well, that's a big negative thing about the iPhone for me. I can't control the shutter speed, aperture, ISO - something that as a professional photographer I'm really used to have and use on my DSLR. Do I sometimes miss this feature on my iPhone - yes. Does it prohibit me from taking pictures - definitely not. And, some apps allow you to control at least some of these (I'm not sure how 'real' shutter or aperture control can be with these apps, so don't take my word on that, please :) ).
(All pictures in this article were taken with iPhone 4s and most of then post-processed with an app on an iPhone)