I understand what DC offset it. It's moving the center of the waveform off of the zero crossing line. Not really sure when you would use it. Is it more of a means to fix things or is it used for other reasons? Is it a common thing to have to use in most people's setups?
Fortunately DC offset is rarely needed, but if occasionally you get files that have been captured on poorly calibrated sound cards, or poor quality recorders then DC offset repair can help, although I haven't had to use it for at least 2 years.
In severe cases the DC offset will shift during the file, then you have to break the signal up into smaller regions before repair, but this is very rare.
In short, if you are using professional maintained equipment then DC offset should be rare, however if you are working with archive material without calibrating the reproduction hardware, then you will use it a lot.