Carrying thoughts around for extended periods of time can fill a lot of mental space. At a certain point it becomes unbearable. One just wants to get the thing done. At the same time going the distance sometimes leads to insights that make it all worth it.
Stravinsky apparently only thought about his compositions while he was in his workroom, something I’ve never been able to achieve with music. It is only when making drawings that my attention is fully occupied with what I have in front of me as long as I’m doing it and ends as the activity does.