I left you helpful links, including a link that discusses the various kinds of matches in this discussion:
https://www.geni.com/discussions/174242?msg=1181869
Green matches can be of great value for some families / populations if you use SmartCopy, assuming that you have many relatives that descend from the same ancestor.
For example, Campbell is an Indiana branch of descendants of my great great great great grandfather. There are good family trees for Campbell on Ancestry and on MyHeritage. Using Google Chrome browser and SmartCopy (a user created tool), I can automatically update my Geni tree with information from other people's family trees or from Find A Grave. You have to be careful because the information may or may not be correct and some trees are quite bad. But if you know nothing about a branch, this is a good way to get a kickstart and then you can follow up with your research or contact people who belong to that branch to improve the tree.