sensors-detect needs to access the hardware for most of the chip detections. By definition, it doesn't know which chips are there before it manages to identify them. This means that it can access
chips in a way these chips do not like, causing problems ranging from SMBus lockup to permanent hardware damage (a rare case, thankfully.)
The authors made their best to make the detection as safe as possible, and it turns out to work just fine in most cases, however it is impossible to guarantee that sensors-detect will not lock or
kill a specific system. So, as a rule of thumb, you should not run sensors-detect on production servers, and you should not run sensors-detect if can't afford replacing a random part of your system. Also, it is recommended to not force a detection step which would have been skipped by default, unless you know what you are doing.
There is (very) low chance of actually breaking your hardware, generally by overwriting some EEPROMs by accident. Some (old) problems that happened with
These issues are very rare, but it can happen, so I'd just listen to the warning and skip the I2C/SMBus scan. Btw. lm_sensors isn't the only thing that can destroy (or damage) your hardware -- Linux (kernel) was bricking LG CD drives in 2003 :-)