One case of 'no problems' doesn't necessarily prove it's fine. You may have been lucky.
3.5" drives differ widely in power consumption. Without making sure the model at hand is (very) low power, it's not a good idea to hook it up to the floppy power - which reportedly doesn't tolerate somewhat higher power HDDs. So, general advice is "don't do it unless you know what you're doing". Enforcing the feeble line is a very good idea though.
