Battery switch use while engine running

Further along in the course it is stated "It is prudent to always assign one “isolated” battery or a bank of batteries for the sole purpose of starting the engine. Never use it for other tasks." This means at some point you must switch from the engine battery to the house batteries with the engine running. However, in the picture of the battery switches, there is a notice that reads "Important: wait for engine to come to a full stop before turning batteries off". I have to assume then that this does not mean "do not turn individual batteries off while the engine is running", but rather "never turn both batteries off at the same time"? Assuming that I'm correct in my above assumption, what is the proper procedure after start (after giving a couple of minutes for the engine battery to recharge after starting) to switch the house batteries back on and disconnect the engine battery? Say 1 is Engine and 2 is house I'm assuming 1 -> Both -> 2 and never 1 -> BOTH OFF -> 2 Is my understanding of this topic correct? Is there any difference operationally between how one would use that displayed in the picture and a 4 way switch, especially since there is no common present with a 4 way switch mounted? Thanks