It is important to understand that there are some very different use cases these days than have been used in the past. With big, slower systems like this, you may only focus once every hour or so, so a several-minute run might not be that big of an issue.
Keep in mind that today there are a lot of CMOS imagers, using smaller systems, often refractors or camera lenses that are more complex optically, which can have a much greater focus shift over time than big, simple and stable systems. CMOS imagers may also expose on the order of tens of seconds, rather than tens of minutes. Many of us also have very large temperature gradients from the time the sun sets to minimum temperature each night, as much as 50-60 degrees or more. We may need to focus every few minutes early in the evening, and no less often than every 30 minutes, to deal with the way our scopes or lenses handle the cooling and how our focus shifts.
In this context, any focus run that takes several minutes to complete (and note, this IS with binning, and this is with CMOS cameras that have very fast downloads compared to classic CCD cameras…instead of 20-30 second download times, ours are usually a couple of seconds) is a focus run that takes too long to complete. Frequent focus is additional overhead on top of frequent dithering, frequent frame downloads, so it is a constant march towards finding ways to optimize and minimize our overhead time, so that we can spend most of our time exposing the night sky, rather than most of our time focusing, dithering, and downloading frames.
FTR, binning or not does not really have any impact on frame download time with CMOS cameras. In my case, with SGP’s native ZWO camera support, it takes about 1.2 seconds on average to download a frame…1x1, 2x2, 3x3…it doesn’t really seem to matter.