not being one of the "12" -- whatever -- perhaps I must be required to clarify....

Stipulated: having the static image in the background won't slow down your render very much.

However, on the premise that the control and post-processing factors I described might have some merit, even though I am not famous....

If you are making a two or three second low frame clip, you probably don't need to follow the professional practice of rendering to image sequence.

If however, you are seriously creating a 'partially animated video' for a serious purpose with thousands of frames, it could happen that you (or your client) may wish to tweak the background after principle render or may wish to insure yourself against computer failure in the middle of the night during a 20-hour render, you may wish to consider rendering to image sequence.

::::: Opera :::::