The juice definitely drains from the atomizer, although slowly enough that we generally don't notice it during the day.
And depending on how thick your juice is, and what filler material you are using, it will also drain a bit from the cartridges as well.
So basically, put that all together, and use common sense to tell you what is best for you at any given time.
For example, if you leave it attached to the battery overnight, standing up, it will drain into the battery.
This is what I do, but I have a sealed battery, so I just wipe it out each morning.
On the other hand, if you leave it standing on the cartridge side overnight, juice might drain down into the airflow channels.
Which means you might wake up the next morning and get a mouthful of juice.
When I was using cartridges, this is what I did during the day...
I would stand my 510 on the cartridge end when it was full.
And I would stand it on the battery end when it was running low.
And in between I would just lay it on it's side.
At night, I would remove it and let it drain into a paper towel.