1) Source? Well, as it has been also written here, I hear that from every IT-Department I worked with at work. Also learned it once the hard way and got a swollen battery. It was an old old laptop (around 2003 IIRC) and old laptop batteries are an own story, but since people want to repurpose old hardware, I think this is a reasonable hint. Also Linus Tech Tips brought this up in one video.
Also, the newer your laptop the better it might handle it, but I wouldn't bet on it.
2) Why? From my understanding the constant on/off charging and heat development (also due to faster dust buildup. If the fan runs 24/7 it sucks a lot more dust into the case) is the problem. Especially if you run heavy tasks over a longer period, the hardware will heat up to a level that it is not designed to do.
I will grant that the lighter the load you put on that hardware, the less all this precautions matter. But my principle is, that if something is not designed (and likely not tested) for something, proceed with caution if you understand what you're doing, or leave it be. So if you want to host your static website on it, you might never ever be near any problems. But I still wouldn't recommend it.
I'm running an Asus N751JX with 16GB RAM. It works perfectly and is a great addition to my small Raspberry pi 3/4 army.
But a heads up for everyone doing this. Please, please remove the laptop battery before running it 24/7. Otherwise this is a serious fire hazard. The hardware and especially the battery are not designed to run under these conditions.
You lived somewhere and are speaking for the whole country... I live in Zurich (the city) since 2015 (and my wife since 2018) and we have the opposite experience. Small talks with strangers and totally open converations with swiss people if you want. But you have to be open for it. If you are an introvert yourself, people mostly just respect that and cut conversation to a minimum.
And yes, Im speaking mostly for Zurich City as part of Switzerland, not Switzerland as a whole.
https://www.youtube.com/watch?v=BY7-sECF3Dw