Inspired by Ron's post here, I'm wondering how necessary it is to top off a carboy of wine that is aging. I have 5 containers of mead/wine right now and they all have headspace. Not a ton but they definitely are not full to the neck.
I imagine the answer has to do with whether or not/how often you open the container to take samples. I don't think I've ever had any major issues related to headspace in my beer/cider but I don't have as much experience with wine. I imagine if it was an issue I'd already be in trouble since this mead has been in there for a year now (as of this past Monday).