What action allows for seamless insertions of media without overwriting existing content?

The ability to seamlessly insert media without overwriting existing content is achieved by clicking and dragging while holding the alt key. When this method is employed, it allows the user to perform what is known as an "insert edit." This technique ensures that the new media is added into the timeline at the specified point, pushing the existing media forward instead of replacing it. This is particularly beneficial for maintaining the integrity of previously edited footage while enhancing the overall project with new elements.

The other options would not provide the same result. Right-clicking to insert clip options would typically bring up a menu for various actions, but it wouldn't inherently allow for an insert action without additional steps. Dragging a file from the Media Browser directly can often lead to overwriting existing content if the correct keys are not used, specifically if the user does not hold down a modifier key while dragging. Lastly, using the overwrite button on the toolbar explicitly replaces existing media rather than inserting new content, which would not achieve the goal of maintaining the original timeline structure intact.