E.g, a great-grandparent would be chosen over a first cousin because a great-grandparent only requires 3 degrees of relationship (all up), while a first cousin requires 4 (2 up and 2 down).
Degree of relationship is a method of measuring how related people are by counting the number of parental links that must be traversed, up or down, to reach someone.
Examples
Parents – 1
Siblings – 2 (up to parent, then down to sibling)
Grandparents – 2 (up to parent, then up to grandparent)
Uncles/Aunts – 3 (up to parent, then up to grandparent, then down to uncle/aunt)
First Cousins – 4 (up to parent, then up to grandparent, then down to uncle/aunt, then down to cousin)
Great-grandparents – 3 (up to parent, then up to grandparent, then up to great-grandparent)