Not every picture or video you take is going to be one you want to keep — many not even one you want other people to see.
That's why Photos for iOS lets you quickly and easily delete pictures and videos to get them off your iPhone or iPad. If you're using iCloud Photo Library, that'll get rid of the content on all your devices and from Apple's servers. If you're not, it'll free up storage on your device. If you make a mistake, you can recover anything you delete by accident or later regret. If it's the picture or video you made a mistake taking, or later regret, well, you can immediately eradicate that too.