Will buy a computer only for running bitcoin-qt and other 27/7 services. Don't want risk put my main computers under uch stress, because all of them contaim things that will be a pain to get again, and are more expensive then a computer only made for it.
Running QT 24/7 would really not (IMO) put your computer under very much stress. It uses very little computing power and very little bandwidth (now).
I think the OP was actually referring to people running a VPS or a dedicated server to be a full node to support the network. It is really not very expensive to run a VPS, they only cost a few dollars per month to run.