the density of your quilting is always dependant on the batting you use- if your batting says the recommendation is every 2"-4" (quite dense quilting) and you only quilt every 6" after a few washings you will find the batting has pulled apart-balled up- made unsightly lumps-
if the batting says the recommendation is to quilt up to every 10" apart it probably has scrim (which is a layer the batt is adhered to) and will not pull apart as easily-
the recommended quilting distance does need to be in all directions- there should not be long sections (longer than the recommendation) left unquilted- such as leaving the sashing strips the length of the quilt not quilted or something like that-
as long as vertically and horizontally there are quilting stitches with in the recommended distances it should be ok-
warn and natural is one that allows up to 10" apart- which allows fairly little quilting- large designs...but you should always check the batting package and purchase what is going to work for the design/density you want to use.