When you are about to copy, you will be prompted to choose between interactive mode and silent mode.
In interactive mode, you will be prompted every time an error occurs during the operation. You will also be prompted when you have a choice to make (for example, skip or merge a list that already exists at the destination).
In silent mode, you can choose the behavior to follow in advance for all the cases that require a decision to be made. You will be prompted to select those options, but once this is done, there won’t be any other prompts during the copy. The silent mode is very useful when running long operations, such as copying a huge site overnight.
You can select "Don’t ask again" if you want to always use the same mode and not be prompted again to choose between interactive and silent. If you do so, this option can be changed later by going in "File -> Options -> General" and setting the "Copy mode" to "Always prompt".