When doing long trips across some of those larger zones with bugger-all flight paths it's nice to be able to take my right hand off the mouse and navigate entirely with the keyboard. This means I can swivel towards the television, someone I'm having a conversation with, or some food. Also backpeddling is sometimes simpler and easier than turning 90 degrees with the mouse, then turning back again one positioned correctly. My WASD works on the main only, and I've got the arrow keys for moving both characters.