How can one plan a class?....you never know who is going show up. A plan would ruin the moment presented by the circumstances.
One of the joys of our art is that there are many ways to present a class.
Personally, I wouldn't dream of rocking up to a class just to do whatever I fancied. I know lots that do and some make a good go of it.
My view is that longer term it falls down a little. Lessons can be unstructured, aimless, favorite aspects get repeated, less favoured aspects can be ignored. Some teachers focus on what they want to do...not what the students need to progress.
Aikido makes you free - so its down to choice of course, for instructor and for students, but I always have a plan, a structure, in mind, if not written out. For most of my junior students this will be part of a larger longer term plan...Scheme of works if you like, which contains goals and targets beyond 'practice'.
Usually circumstances dictate some variance, part of the ability of a good instructor is the ability to adapt a lesson to meet the requirements of the students drawing upon their experience and knowledge to do so.
For me Prior Planning Prevents Poor Performance. Far from ruining the moment it ensures that the lesson includes 'many moments' shared with all.
I guess it depends on what sort of dojo you are, and where you aspire to be, what the aim of the class is.....ultimately what sort of person the teacher is too.
My favoured learning style is via interrelated structures...others learn differently so may favour a different delivery method.
Isn't diversity a beautiful thing?