Unless you can find some reason to have the basic feeder open I would suggest you keep them closed unless of coarse you like juice leaking while filling.
I finally think I have figured out what purpose they might serve and that would be to be able to wick up the very last drop because of how high the lowest part of the wick is to the bottom of the tank. I keep mine closed but on a couple occasions I vaped it dry so I see no reason for them except to cause leakage during filling.
Wait you are talking about the basic feed or the nut in this post ? I leave my basic feed on since I got it - I doubled up the Orings on the 510 post so now it doesn't warp when screwed in to the base