Currently, when you edit a global approval process that is already in use, your changes affect all objects throughout the system that are already associated with it. If you add a new approver to the current stage on an approval process that has already started on an object, the process for that object resets and the approvers have to start over.
This makes it difficult to maintain updates to global approval paths without affected objects that are in progress. For example, I have a case where a team leader has been promoted to another department. I now have to remove him from an approval path, and add his successor, however there are close to 80 items that have already entered the approval path, and which will now be reset for all the previous approvers to have to 're-approve' the item.
My work around is to create a new approval path, and link the queue topic to the new approval path so that any new items are linked to the new path, but it would be nice to be able to govern whether you want all objects to be reset, or not.