When the Space Shuttle launched, it would perform a roll and then pitch to establish its ascent trajectory. There is fairly straightforward rationale for this. The vehicle's aerodynamic shape, the benefit to keep the horizon visible through the flight deck's upper windows being the most obvious.
Flying long before the Shuttle, the Apollo launch profile has been described in a very similar way - a roll to orient the vehicle so that a pitch maneuver puts it onto trajectory.
My question is this: With no large-scale external features to break the vehicle's apparent radial symmetry, why was it necessary/preferred for Apollo to roll first then pitch instead of forgoing the roll and simply yaw or yaw/pitch? Since the net thrust and drag forces are aligned with the vehicle's long axis, would it make any difference which way the vehicle is oriented in roll? Were the considerations similar to Space Shuttle (despite the capsule windows being covered until escape tower jettison)? Did Mercury and/or Gemini do the same?