sometimes you have empty tracks in the middle of the first and end tracks which they are also rendered and causing hdd space and time and effort for importing them to daw, so in the rendering window, perhaps we can choose each track individually which tracks to be rendered and which not.
How do empty track take up harddrive space when you render to wave?
Wave file size is a funciton of the length in units time of the song, not how many Renoise tracks it’s composed of.
I would assume he is rendering each track as a seperate file so that more work can be done on indevidual parts in mastering type processes.
If the track isn’t used just delete it 
Mid-song quiet points I guess you will just have to live with 
yeah , sorry i didnt state that its in “save each track to separate file”
deleting the track is also an option, still i would be glad like a window to select which individual tracks to be rendered