Not all flavors of Atom CPU support frequency scaling, as Sven Gaerner found out. This means more heat and more power usage. There’s further details scattered through the thread, but Sascha Wildner found what seems to be the definitive answer of which variants do and do not.
A running description of activity related to DragonFly BSD.
I have FreeBSD on a small Atom D510 machine, and powerd does indeed do frequency scaling with the p4tcc cpufreq driver. Most of the time it seems to keep the CPU scaled to below 800MHz. The system does put out a little heat, but not very much, and it’s completely fanless. According to coretemp, idle CPU temperatures are about 50C.