Well, the first part of the quoted sentence is fine (Search and rescue teams don’t want to create “an incident within an incident” ) A searcher who themselves becomes injured or lost has only added to the problem. Whether or not to send searchers out in the dark is (or certainly should be) a case by case decision. It depends on the nature of the search, urgency, weather, moonlight (or lack therof), and terrain.

The first question to ask is how much additional risk does night searching involve? In some terrain, it might be quite reasonable for experienced teams to move around at night. On the other hand, in some areas searching at night might add unacceptable levels of risk to the searchers. For example during periods of high avalanche danger, it may be very risky to send searchers into areas when they can't clearly see and evaluate what is above them. It depends.

The second question is how effective can the searchers be at night? Again, it depends. In darkness searchers might miss (or even trample) subtle clues, meaning the same area will need to be searched again in daylight. On the other hand, some clues (foot prints for example) might show up quite well with low angle illumination from a headlamp. It depends.

Note that a "search" doesn't just mean thrashing around in the brush. A good search manager looks at the big picture, and come up with a sensible strategy and tactics for each operational period. In reasonable terrain, one might continue with active searching after dark. If nighttime searching looks to be too risky or ineffective, one might suspend walking teams till daylight, but still continue other tactics. For example you could post people at trail junctions and other choke points ("containment"), and build big bright fires at other key spots ("attraction"). Or you might choose a combination, and continue ground searching in "Segments 1 & 2", but wait till morning to search "Segments 3 & 4", and also maintain containment at key spots. And some kinds of aircraft searches such as infrared actually work better at night. It depends.

Bottom line is, as always, it depends.