Headspace in Secondary

I just read some guy's posting about how important it is to having zero headspace in the secondary. Is this true or just a myth? I've made about 6 batches of beer and always had a fairly large headspace and never had any issues.

It's obvious that you'd get headspace when transferring because you're leaving all the trub behind. Are you suppose to compensate that space with anything? I'd hate to think that you'd add water..

Thanks!

First, this is not an all grain question so why post it here? This is a pet peeve of mine.

It depends on how long you leave it in the secondary. The air space will eventually oxidize the beer. If your gonna secondary for several months this is a concern. For the same reason it's important to use glass for the secondary. Plastic is too oxygen permeable for long term storage.

Lastly, Why secondary? What are you hoping to gain from the secondary?

The concern is oxidation. As mentioned, the longer the more concern. If you have CO2 laying around just gas the space out before installing the bung. If you don't then DWRHAH

What I get out of using a secondary is a very clean beer. I get compliments on how clear my brew is without even filtering it.
And.. I like to add dry hops to my brew so I don't want all the hop pulp mixing in with the resting Yeast.