is EF 50mm f/1.2L a good lens for full body portraits?

If you carry a lens in your pocket or pouch on your belt and use the one handed lens switch method, it can be pretty quick. Event photos where you are shooting groups, you probably want a deeper DOF and the f/2.8 is not really an issue. If you are a wedding photog and are doing bridals, you may want to shoot at f/1.2 in some instances

If you shoot a person 6'5" full length you either need to be at...

• 7' distance using 35mm on FF, to capture 7.1' x 4.7' area in the frame, with DOF zone at f/1.4 of 4.3"
  
• 10' distance using 50mm on FF, to capture 7.1' x 4.7' area in the frame, with DOF zone at f/1.4 of 4.3"
  
• 17' distance using 85mm on FF, to capture 7.1' x 4.7' area in the frame, with DOF zone at f/1.4 of 4.3"