When we say length we are either talking about long or short answers. It doesn't matter as such but to some degree it's important because there is no how you can answer some questions perfectly for people to understand every bit without breaking it into reasonable pieces .
If you are answering a question that needs explanation and you didn't put any effort to explain to the latter, it won't make enough sense and this will affect the percentage of the vote that will be received or get no vote at all.
From musing post guideline ,what makes a quality post was outlined and one part explains this. I quote
"Quality answers do not have a minimum length but providing insight and elaboration to a yes or no answer can be more helpful"
It shouldn't. How useful or correct the answer is should determine if it will be upvoted or not. One could say a lot and say nothing meaningful at all.
It depends. I have noticed since the new delegation that answers are becomign longer and more thought out. Longer is not nessasarily better - sometimes the best answers are short and to the point and can answer the question.
However, I have also noticed that people who go the extra mile, and do extra research, and consider all angles of the question are consistently getting the best upvotes. This is why I find it best to stick to answering questions that I actually know something about, so that I can offer my experience or my own personal view