The RCC is part of what allows you to control multiple drones simultaneously, from what I understand of the chapter. It also provides better protection for your drones; an RCC can handle up to Device Rating x 3 drones slaved up to it, while I'm not sure how many a commlink or 'deck can have. In addition, RCCs let you choose the better of your stats or the drones for defense tests; the example used is your Willpower instead of its Device Rating, if the former is higher.
For defense test, you either use your Reaction + Intuition + Control Rig while jumped in or using remote control, or you use the drones Pilot + Handling when running on autopilot. It is NEVER the better of the two as situations will change.
Jumped in > VR Remote > AR Remote > Autopilot
You need an RCC to run multiple drones and issue commands to all of them in one simple action. If you want to tell five different drones to perform 5 unique tasks, you cannot do it with just a normal commlink or cyberdeck using the Control Device action. This is what makes a RCC important for Riggers. Also, you can always slave an RCC to a Cyberdeck or Commlink. You can also run drones on Commlinks and Cyberdecks, but you're limited to device rating and giving orders as complex actions.