DJI Phantom 3 prop guards are not a must but they do provide several advantages.  For starters, DJI Phantom 3 propeller guards make the risk of breaking a propeller due to bumping into a pole, etc. less likely. Also, they better prevent broken props if the Phantom 3 falls on its side after landing.  Since these are quick-disconnect prop guards for the DJI Phantom 3, they snap on and off quickly without tools.  They will fit alongside the DJI Phantom 3, controller and other accessories within the DJI phantom 3 waterproof and ruggedized case that I use.  Since these quick-disconnect prop guards became available, I refuse to fly without them.  It’s great not having to buy DJI Phantom propellers so frequently and it promotes safe and responsible drone use.