It's called a clutch system because it technically engages and disengages the main engine cooling fan. That's where the clutch term comes in. Viscous because the engagement is done by the silicone gel inside the clutch that uses friction to engage the fan.

Basically there's a metal blade in front of the clutch. If it gets hot, it expands, right? When it expands, the metal tab bends a little, letting the small pin out from its hole. This pin is like a gatekeeper that allows the viscous fluid to flow and "engage" or "bite" allowing the fan to cool the engine when it gets hot as in the first condition.

So as you drive faster that cools the metal strip in front of the clutch assembly, which makes it straighten up from being bent, so it pushes the pin back inside and the silicone gel goes back to where it came from, disengaging the clutch at high speed because it's not necessary for cooling the engine (primarily because the airflow is significant enough to do that job).

My best guess is you'll need to test it out yourself, some clutches have different capacities than others.

When the engine is cold, the fan should not engage. This allows the fan to "slip" and not bite the clutch, allowing the engine to warm up faster. When it gets up to temp, it engages to cool the engine, when it gets cool once more, as in high speed drives, like I mentioned above, it will release the clutch once more and allow the air flow to cool the engine instead.

When in traffic, that's where the auxiliary fans come in. Most cars today have two, one for when the AC is in use and another to cool it down when it reaches a certain high temperature. Or perhaps it's slightly different for other makes.