At the end of Back to the Future (part I) Doc appears on the time machine right near the Marty's house and tells Marty to go with him rescue his kids. They also took Jennifer with them. However when Doc uses sleep inducer on Jennifer in Back to the Future Part II Marty asks what they brought her for. Doc answers that she saw the time machine and he could not leave her with that information.
Does it make sense for Doc to appear at the front of Marty's house at all? How did he know that specifically at that moment there would be nobody on the street apart from Marty? What if there were Marty's parents, siblings, Biff or even dozens of neighbors to witness the flying DeLorean? Doc could have appeared at the lake where there are likely less people.