wind bars and smoke are often what can help bring together a bigger piece. Some Japanese back pieces in progress look really weird to me until those wind bars are dropped in
I like filling as I go. 'Negative' space is only 'negative' if it's in the foreground. Good background fill is imporant, and gives the tattoo a frame of reference and it gives the viewer a sense of time and place.
I am more stringent and particular about an artist's smoke, clouds, wind bars, water then I would be about skulls or hanyas, dragons. It matters.