Remove DC Offset

Could someone please explain what ‘Remove DC Offset’ is all about. If I apply this effect to a track I get a progress bar which travels quickly from start to end, fine, but then I can hear no difference in the track afterwards. Specifically, I should be grateful if someone could explain: (a) What DC offset is, (b) How I know if I’ve got a DC offset, © Why it needs to be removed, and (d) If it needs to be removed then why is it a selectable function which implies that you can leave it there if you want. If it’s bad and needs to be removed then why isn’t it removed automatically from all tracks out of sight and out of mind?

Thanks in advance for a quick lesson on DC offset…

http://www.harmonycentral.com/docs/DOC-1082