While the Supreme Court justice authoring the opinion will have laid out the broad principles and legal framework upon which he/she wishes to make the decision,

While the Supreme Court justice authoring the opinion will have laid out the broad principles and legal framework upon which he/she wishes to make the decision, the law clerks have a central role in crafting the opinion and making sure that the arguments and reasoning are sound. By the very nature of the court's operations, the justices cannot be writing the 30 page opinion and doing all the research on every case. The clerks are the ones who will be writing most of the summary, determining how certain cases influence the current case, and laying out the draft logic. They'll have many sessions with the justice to test the logic and find edge cases, implications, and make sure that a decision affecting millions of people is sound. Basically debate and draft/redraft the opinion (with other justices + clerks as well) based on what they're finding as the drafting continues. I would say the clerks are indispensable to the creation of the opinion's outcome.