I'm a fairly new owner of a 3600x (motherboard: B450 Tomahawk Max) and for the short time I've been using it some of the cores used to go to sleep when I wasn't doing anything serious in the system. As of a few days ago however, none of the cores are going to sleep anymore (It may be because of a chipset driver update but I can't say for sure).
Windows will distribute all background tasks evenly on every logical core. This is a nasty behaviour. I use a software named "process lasso". So i can bind all background tasks on 2 logical cores (1 physical core). In addition this software switches to energy save profile when your pc is idle. This will save a lot of energy.