There are some pros and cons to using iCloud Keychain. For example, it doesn't have a separate master password option, so once you unlock your device, anyone you hand it to can access all your passwords and credit cards. Also, the passwords it generates aren't particularly strong. It is, however, easy and far, far, better than nothing. Apple will ask you if you want to use it when you first setup your iOS device, but if you change your mind, or if you want to switch back or switch away, you can quickly enable it - or disable it - in Settings.