[throw20102010]

You can use it at stock speeds with passive cooling, but you can also use it at below stock speeds (just change the numbers in the tutorial). The main benefit not being cooling, but lower power consumption. Lowering speeds is fine, but under volting often causes boot errors, so I'd stay away from that.

[et2o]

I've been reading that the Raspberry Pi 4 tends to run very hot. I saw reports as high as 80 deg C with the case and no active cooling.

[throw20102010]

80C is warm, but not life-threatening to the chip. I'm not sure, but it may start to throttle at this temperature, as previous versions did throttle at 80C. So cooling is helpful, but not required (Apple ran inadequate cooling in their MacBook Pros for years). Also, I think that hitting 80 is only under heavy load. Regular use should be cooler than that.

You will certainly need to cool the chip to get any meaningful overclock. In that case it is different from previous versions of the Pi, when you could overclock a bit with no extra cooling at all.