I have some very old, very well used quilts that were tied.
The important things to me with a tied quilt -
1) The knots are secure
2) Depending on the batting/filler/middle - there are enough knots to hold it together and to keep the middle layer from shifting around - if one is using flannel or warm and natural batting, for example, one knot every 10 inches would probably be adequate. If using a fiber that is sort of 'loose' - a knot every four inches - read the packaging label
3) I prefer the knots to be 'arranged' - not scattered willy-nilly. It probably doesn't affect/afflict the utility value of the item, but I like the knots to be arranged in fairly straight lines and fairly consistently spaced.