I’m objectively opposed to having a detailed plan for the musical accomplishments of a rehearsal.
Let’s be clear: I am specific and detailed in the plans I make for rehearsal, with regards to music being rehearsed (often down to specific bars), for how long, and benchmarks for ensemble growth.
What I don’t plan is the specific musical decisions. I actively try to not have an opinion walking into rehearsal about whether there will be a breath at a specific point, what the final tempo will be, who will sing a solo, etc.
I do have ideas: I’m an experienced conductor and have strong musical opinions. But they aren’t the only musical opinions, and what would work for another ensemble might not work for my ensemble, today. (We also try to establish “factory default” musical choices that will work for most scenarios.)
So we are making decisions together in rehearsal, and I hope I am modeling careful listening and assessment of the ensemble and of the opinions of ensemble members. (It also means that I am modeling marking my score as I rehearse!)
It’s harder work for the ensemble – it’s a lot easier to be given the decisions than to think and make the decisions together. It’s also a lot more time – at least at first. But my long-term goal for any student in an ensemble I direct is for them to grow into a musician capable of assessing music and making musical decisions for themselves. I don’t know how to do that if I’m also always enforcing my musical will and interpretation on them.