Good example of this is the 4 watt limit for CB radio transmission. I remember being a kid interested in ham and CB radio as a kid and being blown away seeing someone's "illegal" 300W amplifier.really doubtful that the FCC opens many investigations over that.
CB Channel 6 is still an ongoing cultural phenomemon. Now that it's the summer, it's back alive with 10kW transmitters all over the place. Today not a single channel was empty, and there was a lot of lower sideband, and freeband operations going on above CH40.
I know a guy in my neighborhood who has a old beat up GMC suburban, with a CB radio, a 5kW "12 pill" amplifier, 3 alternators, and 2 heavy-duty CB antennas installed, and he goes by #1 on the air. Guys like him still participate in CB radio shootouts like this: https://www.youtube.com/watch?v=EyAqzFXDMys
All the while the FCC doesn't bat an eye. This is because they typically don't cause that much harmful interference. Even though the transmitters are often overdriven and non-linear, typical spurious emissions are outside of critical communications bands and aren't the source of many RFI complaints which drive a majority of FCC investigations.
Another example is PMR, aka. walkie talkies. In many countries, you can use the PMR frequencies unlicensed only through radios with non-removable antennas limited to 0.5W of TX power. Doesn't stop people without licenses from buying and using handheld transceivers intended for HAMs and professionals (like the popular UV-5R with 5W of TX power and a removable antenna) on these frequencies.
