Knowing how you want it to end is extremely useful. I knew I wanted a TWOK funeral and a Kirk voiceover. I knew I wanted a TSFS destruction of Enterprise. These present great problems. The series has trouble going forward and It's a hell of a downer of an ending. "We'll meet you at the rendevous on Tatooie." is about as important as "I am your father." and I love you/I know. It reminded the audience that there was hope and something to look forward to at an important moment. I wanted everything in STID to follow the philosophy ST09 and be bigger, faster and more spectacular. Kirk's sacrifice had to be for much more than ship and crew. Same for ENTERPRISE. Working out the ending in detail showed me what sort of "Chekov's guns" I needed to plant earlier.