A former instructor of mine in Bridgeport, Connecticut, David Faile, taught me to use the two comms for different phases of flight. I'd do all the ground stuff — ATIS, ground, clearance and the like — on comm number two and all the air stuff in comm number one. So before flying I'd handle the ATIS, clearance and ground chores on two and then simply swap comms when it came time to go to tower before takeoff. I'd already have the frequency for departure in the standby so all I had to do was flip the switch. One less thing to do on a busy phase of flight.