Maybe I did not express myself clearly.
Yes, when performing (or rehearsing with the band), I find it important to use my eyes to communicate with band mates, with the audience, to look at some sheet music, and, yes, also to help my left hand finding the notes on the fingerboard. So we agree on this, I believe.
The point I was trying to make is something quite different. It is about practicing alone by myself. This is a situation where there is no need to use my eyes for communication. Also, since I play fretless instruments (mostly double bass, but also fretless acoustic BG), (a) there is much to look at on the (unlined) neck, and (b) good intonation is a never ending challenge. In this circumstances, I find (and I could well understand that it would work differently for someone else) that closing my eyes intensifies the clarity of my hearing (somehow like how vision improves when some fog disappears). This pertains both to intonation accuracy, as well to the connection with musical ideas I pre-hear in my head. It also helps constructing a mental map of where the notes are located on the fingerboard.