Unless you have been living in a cave since the early 90s you know that cyber security is a huge issue and that you should protect your data as well as you possibly can. If you are sending private information in documents and spreadsheets over the internet via email, Dropbox, iCloud or any other service, it becomes vulnerable, regardless of how secure you think the medium is. And who knows how the recipient will handle the info?
A long time ago, the Apple ID was like any other username. But nowadays Apple requires all Apple IDs to be verifiable email addresses. Since everyone's Apple ID is an email address, many of these have been found in data breaches and leaked online. While your actual iCloud or iTunes accounts may not be compromised, the email address you use for your Apple ID could have leaked along with billions of other account records.
iPhone, iPad and iPod touch owners have been warned about a FaceTime bug that was recently discovered, which could affect privacy. In a nutshell, FaceTime callers can hear audio through your iOS device's microphone while it's ringing. The would-be eavesdropper has to follow a few steps to unlock the bug, however anyone receiving an incoming FaceTime call could be at risk, before the call is answered.
If you use Instagram you probably share your Stories with family and friends, and probably don't want them shared with people you don't know. Your friends and family, however, can share your stories with others as direct messages. If you have your account set to private it doesn't matter because only your followers will be able to view it, even if it is shared as a direct message.
Siri enjoys delivering answers to iPhone owners whether their devices are locked or unlocked. Sometimes the call "Hey Siri" is even answered no matter who is asking. Pressing the Side button or Home button can also invoke Siri from the Lock Screen. For those who consider this a privacy or security risk, Siri can be completely disabled when the iPhone is locked.