What is it?
If you have a profile in more than one Tree, Tree merging will allow you to merge these two profiles. If others nodes in the merged trees are duplicated, you will be able to merge these nodes, creating one combined, accurate record of your genealogy using the information in each tree.
This enables the combination of separate Geni trees into a larger tree. (In the future, you will be able to use the GEDCOM import feature to merge your GEDCOM data into an existing family tree on Geni.)
Tree Merging extends profile merging by allowing you to merge your profile with a profile on another tree using a request system for the necessary approval.
Later releases will refine these features and implement more complex ones.
The order you choose to work on them has a profound affect on other merge issues, and the time it takes to get through them. When merging two entire otherwise identical branches, it was almost always more efficient to start with the youngest generation and work your way backwards in time, progressively toward the ancestors. When you do it in that order, the tool usually lets you take care of entire sets of siblings and their parents at once. But if you start with the parents, the tool usually (maybe always) doesn't know that children with identical names, birth dates and dates of death could possibly be the same person.