Allow Closing

Check "Yes" if you want the viewer to have the option of closing the In-Video Ad (by clicking on the "X" closing icon in the top-right corner of the ad, or by hitting 'Esc' (escape key)

If you don't check it, that means viewer will not able able to close the Ad.

Which means, you should enable it to Auto Close. If not, the ad will be stuck on screen,a nd the viewer will not be able to continue watching the video any further.