I don't think I worded this very well. Let me try again: Assuming you have a quilt that is more than 45" wide x more than 45" long, would you cut the border fabric along the length (even though that would decrease the 45" width of the remaining border fabric) or would you cut it from selvage to selvage and piece it?

If I am making a very nice quilt, say for a wedding gift, I will buy enough fabric to be able to cut the borders from the length of the fabric, so that I don't have to piece them. If I am making a utility quilt, say for a grandchild to drag around, I will cut the borders WOF, and piece them.

Buying enough fabric to cut the borders w/o piecing adds to my stash, so it's a good thing.

I cut stripes either lengthwise or crosswise depending on which way I want the stripes to run. For other fabric, I prefer the cut lengthwise so I can avoid seams and will do this if I have enough fabric. Otherwise I cut crosswise and piece on the diagonal.

depends on the quilt and the border fabric- sometimes i cut the fabric lengthwise- if using a border print- or when i don't want the borders pieced sometimes i cut the fabric across the width and piece it- every quilt is different- and needs a different border treatment...do what works for you and your project.
it also depends on if i have enough fabric to cut lengthwise-...

Lengthwise to avoid seams.

Having said that, though, I'm quite a fan of pieced borders and have been using them more and more frequently.

I cut selvage to selvage and piece. This is usually, for me, the most reasonably economical way to do it. I don't find the seams an issue.

Lenghtwise is my favorite way to make borders, sewing on the top and bottom first and then the sides.

I also do it this way, and I use 45' angle seams like binding.

I cut WOF for borders, but I do more pieced borders than plain. I don't think the seam is a real problem, but if it bothers you then cut the length. It's your choice, no rules.

I cut WOF and piece, sometime with a diagonal seam, especially if they are narrow.