Before you start working on any project, try to determine the hierarchic structure of the people who work on it. On most film projects, the director should be the highest and last instance for creative decisions but it occurs from time to time that one of the producers or someone else is the one who decides.
Sometimes, these structures are not really clear or not even properly negotiated between the parties involved so that several people feel like being in charge. Any situation where you as a composer don’t have one specific person to have the last word on your work has the potential of becoming a nightmare – especially when several parties disagree on the music. Doing rewrites until everybody is happy is extremely annoying and time consuming and will easily torpedo any deadline or workload predictions you made beforehand.
On projects where the hierarchical structure was unclear or the final decision is shared between several parties I generally try to argument for one person taking over the musical decisions usually argumenting with “If we do it like this, the deadline can most likely not be met as from experience I know that there will be misunderstandings and several instances of double work.” Questioning the deadline is one of the biggest scare factors for directors/producers so chances are quite high that you will succeed with such an argument.
Unfortunately, sometimes the most valid arguments will not help and you just need to chew through a split up hierarchy.