These are machines that have additional computer based functionality outside of the base function of the machine. They come in many different varieties, from LED lights that are controlled with a phone application, Television sets that have online components through to remote access cameras, voice activated "assistants" that send all audio to external servers for analysis - regardless of the base functionality, they all have the same issues.
Running non-free software these machine work for the companies that make them and not you the supposed owner. You get some input on the machine but ultimately you only have as much control as the proprietary software developer allows you to have. Without the ability to study and modify the software that these machines run, there is no way to know exactly what data they are collecting, what security risks there may be or even what is potentially possible of the hardware both good and bad.
Smart watches and exerciser assistants can track peoples location and behavior. TV sets can track what people are watching and some even listen to what is being said near the TV or force additional advertising content onto the screen. Voice assistants records and catalog everything that is said in the vicinity of the microphone.
There is also the issue of ethics that comes into play. A lot of this information can be collected on children without the – this would normally need an ethics committee to approve something on this nature but because it is done via a computer that is voluntarily purchased they are seemingly exempt from this. We should not tolerate any surveillance of this type no matter the form it comes in.
While not all IoT machines are directly restrictive, the vast majority sold today are. There has been a push recently to make devices that are powered by Free software but we are at just beginning. The large variety of devices and hardware specifications has made it a very difficult thing to tackle. That said there is progress being made. A good example is the Mycroft voice assistant that can perform all the same functions as the non-free spying devices but all the processing can be done locally on your own PC using free software.
As enticing as these devices are designed to be, the hidden cost of your privacy and freedoms should never be traded away for mere conveniences. The long term cost to you personally will be a much bigger issue than the short term gains on speeding up a few very trivial tasks.