What is DC offset on the AC power line?

Thanks. The article is rather comprehensive, and while it explains a common cause could be an old household appliance, the article does not indicate what the disadvantage (if any) would be in using a DC offset filter if you didn't have an old appliance or otherwise need to. There must be some disadvantage in using this type of filter and that is what I'm looking to understand. If there is no disadvantage, I'm curious why the filter wouldn't be more widely available.

the link u are providing is a forum thread from 2002 with many pages. I glanced over it. I do see one notation " What I'm trying to say is that the capacitors could limit the current and thus prevent the fuse to trip which may lead to dangerous situations. " 

jea48, here is an alternate url
http://emotiva.com/products/accessories/cmx-2

thanks for your continued feedback

wolf_garcia, thanks for that post. Obviously use of that kind of filter can "work" (have the intended effect of reducing hum). Actually, they describe rather well what I was looking to understand.
http://www.psaudio.com/wp-content/uploads/2011/11/HumbusterIII_-Manual.pdf

jea48, no, I am not currently experiencing a loud mechanical buzz or otherwise think I would need such a device. However, in the past using a Carver MXR130 on the same outlet I have my current M6Si the Carver transformer did have a hum. Besides the PS Audio Humbuster III posted by wolf I wasn’t sure if this was something perhaps widely used in a audiophile grade system. But it’s because I do not have a problem that I’m looking to solve by virtue of a DC Filter that I’m asking what the drawback of using one is. Perhaps my electric system emits a "noise" of some kind amplified by the audio system and I merely cannot hear it. I doubt it, nevertheless, a possibility. Its also seems conceivable that a filter of some kind could eliminate or reduce something "unwanted" whether or not a person can detect it from an audible perspective. So again, this begs the question that why wouldn’t a DC Filter be used more widely in an audiophile grade system?

thanks to all who have responded.

davehrab, so here is a question perhaps you can provide an answer for. Your explanation is very good. Suppose that one does NOT have any electronic device with half wave bridge rectifiers and therefore would not have a DC offset problem. What is the disadvantage (if any) in that case if one were to use a DC offset filter (i.e. use the filter in a scenario where there is no DC offset to correct)?