There's not necessarily a safety implication. However with most, if not all airlines, the bottom line is personal electronic devices can be used, but during the cruise phase of flight only, ie. not during take off and climb, descent, approach and landing, and of course when engines are running on the ground.
Cabin crew are well within their right to request you don't use PEDs - especially cameras, but you'll usually find they're quite happy for you to use them. It makes life easier if you don't question their requests - the onboard crew are the ones in charge whilst you're in their care