Have you ever used a social media app on your iPhone while using the bathroom? ?
Congratulations!
iPhone apps with camera permissions can potentially record each and every activity of your life and even upload them.
Once you grant an app access to your camera, it can

• access both the front and the back camera
• record you at any time the app is in the foreground
• take pictures and videos without telling you
• upload the pictures/videos it takes immediately
• run real-time face recognition to detect facial features or expressions

Without any indication / LED lights!
Checkout these findings by Googler, Felix Krause.

(more details here).