This is where judgement and balance have to come in, Bunga. We have to be flexible, but also have to have a rough plan. Setting up the correct RW in the FMC and navaids are the plan, and that can be changed to a visual (or kept such if that was the plan already) if things get changed. For example, getting 10 mile shortcuts with 35, now 25 remaining miles by being vectored for base leg instead of passing through the centreline to join a distant hold and descend there are the sort of flexible things that should be easy to handle, not requiring a new brief, but some pilots think that needs a full rebrief and there just isn't time. This is where pilots need to be familiar with using the basic AFDS modes and hand flying, and familiar with the performance of their aircraft, rather than needing to consult charts and calculators. That thing they called airmanship. But having no plan for the arrival at all gives you no way of seeing whether things are working or not.