What is the purpose of the roll maneuver on a rocket? I have watched several videos on both rocket launches, ballistic missile launches, even a really cool one by Northrup Grumman on launching a nuclear missile.
(https://www.youtube.com/watch?v=HWZXinRwCaE)
I understand why missiles have a pitch maneuver.  I have watched videos such as (https://www.youtube.com/watch?v=kB-GKvdydho) that state that they roll to cancel out the difference  to match its azimuth.  But could not a second pitch maneuver actually accomplish as well?  The Falcon 9, and Electron don't need to do a roll maneuver, and the Falcon Heavy cannot due to only having 2 boosters attached that have to stay perpendicular to the ground.
Why do non-boosted or basically round rockets, need to do one?
 A: When I was teaching physics, one of my students was an intern at NASA.  I asked him the specific question of why the space shuttle performed the roll maneuver.  He talked to NASA personnel, and reported to me that the maneuver was performed in order to turn the shuttle antenna towards the ground so the astronauts could maintain communications with mission control.
A: 
But could not a second pitch maneuver actually accomplish as well?

The pitch starts the rocket pointing in the correct horizontal direction, and it sets up the correct altitude profile.  But that doesn't mean that the right side of the vehicle is "up" during the climb.  A particular attitude may be driven by antenna placement for either ground or space communications, or symmetry.

the Falcon Heavy cannot due to only having 2 boosters attached that have to stay perpendicular to the ground.

In fact that would be a good reason for it to perform a roll maneuver.  If the track was not already aligned with the perpendicular (Z) axis, then it would need to roll so the boosters stayed horizontal when it was time to pitch.
As an example, the space shuttle launched in an "orbiter down" attitude.  (There was a consideration for it to fly "orbiter up" for some missions, but was never done).  Flying with it to the side would have put undue stress on the connection struts.
But the shuttle used launch pads that were built years before it was designed, and the flame trenches meant the solid boosters could only be aligned in a particular way.  So the orbiter was on a north-south alignment, while the launch track would be to the east.  This required the stack to roll the orbiter to that direction before pitching over.
