It's up to you, you certainly don't have to. Most people can't help themselves I think, but others feel like it's better to do it so you're not incubating quitters.
You'll only see the egg fill with darkness and might see the chicks move but not much else.Ok. So if you're at the veiny part, what would you see past day 14 if it quit? When the chick was bouncing around it was obvious, but now not so much.
The only egg that is (still) worrisome at this point is the olive egger. I can faintly see the air sac in the top, but the one side longways is dark, and the other side longways is light. But I can see the new veins where there weren't before.