Vape to Zero means, holding the breath till nothing comes out. I wonder if this is healthy or not or if you taste more or less if you do it? Is it more enjoyable if you blow it out? Will you loose much? Know you the feeling of liquid resin in your lung and breathlessness after vaping? Is this really healthy or only healthier than smoking?
You can hold it in for quite awhile and its fine, but going super long probably isn't actually good for you, as you will suffer mild oxygen deprivation. I doubt its a huge factor and may be almost 0 harm, but it is something that could be considered.
Hold it as long as you want, there's no tar in there so it's not going to hurt your lungs being in there longer. You are however holding hot air in there which can cause irritation and coughing as a natural reaction. IMO if you "ghost" 1 vape bag, it's the equiv of just inhale/exhale of 2 bags.