Take M31 or Orion as examples of targets. For the example I can use an ED127 w/952 focal length, but to capture fully I would need to make a 3x3 or 4x4 mosaic and combine in PI.
Alternative would be to use a shorter focal length to capture fully the object.
If my objective was to get the fullest detail, I am interested to know and understand why I would not use the ED127 and mosaic the image (knowing this would require 9-12x the length of time to capture is irrelevant for this scenario). Camera could be Nikon APS-C, ZWO ASI2600MC or 2600MM LRGB if that factors in any.