When I first looked through the SCT I was impressed by the image moving about and drifting in focus when attempting to focus. I first tried to six this problem with the electric focus motor. This did not help. I found shifting image and difficulty of finding and holding focus very annoying. Thus I got my first JMI focuser.
Standard procedure is to set the focuser at mid point as described above.
The main mirror is now locked at infinity and all focusing is done with the JMI focuser. For CCD imaging, I use prime focus, 0.63 reducer with the ST-7 or possibly the 0.33 reducer. Basically after a major equipment change I do the centering of the JMI and infinity focus and locking of the main mirror. For remote focusing the DRO is essential since it tells you exactly where your focus tube is set. There is no substitute for knowing where the focus tube is set to the 0.01 mm.