Doing the old trombone shot on a dolly would need focus pulling whilst zooming in and tracking back (or vice versa!)

Kinda strange indeed, but sometimes you DO need to, depending on the job. For example, I worked for several years for Gavel to Gavel Alaska (which is our state's version of C-SPAN). It is produced by the local PBS station and has live coverage of state house and senate floor proceedings, committee meetings, governor's press conferences, joint sessions, addresses by our national congressmen, state supreme court hearings, and any number of other political meetings. The catch is, that these are (with very few exceptions) ALL......live ONE camera shoots. So indeed, there were many times when I had to SMOOTHLY pan or zoom from one speaker (right in front of me) who has just sat down, to another (who is in the back of the room), at the same time that I was racking focus. What is really fun, is in the committee meetings with windows when you are having to pan and/or tilt and zoom, at the same time that you are racking the focus AND riding the iris! You feel like you need as many arms as an octopus!!! But after you've done it a few times you can actually do it pretty smoothly believe it or not.