Seen it done many times. I am not sure that I am correct but some people find it to be risky. Reason being is if the power goes out or you trip a GFIC, the siphon is still going and pulls excess water into your filter and it's not pushing anything out. Not sure its really an issue but I know some people say it's not the best idea.
This is not an issue at all. That's not how physics works. The filter loop holds as much water as it will ever hold. In the event of a power outrage it just stops flowing just like any other filter setup.