I was trying to convince an IBM support tech on the phone that a tape back up unit on a client site was faulty.
Typically he didn't believe me until I sent him this picture. I had a brand new chassis on site the next day.
Another time I had a network outage on a remote site. Long story but I suspected the fiber optic cables were faulty.
This photo confirmed which patch cable was faulty... You can't see the "lavender" laser light with the naked eye.
Honestly I don't know how I could do my job without a mobile phone to take pictures like this.