I believe the "Bottom-Up" approach is important for patients in the acute phase of rehabilitation because those key impairments must be addressed which impact overall function. These include managing spasticity, strength, range of motion, and cognitive deficits. These are key components which allow the patient to move better.
In regards to occupational therapy, current research currently supports a top-down approach such as using task-specific interventions. However, current practitioners continue to use a bottom-up approach, using weight bearing, PNF, and NDT techniques (I speak based on what I have seen and experienced, anecdotally of course).
Neurorehabilitation is a field we still have much to learn about, and it will be interesting to see how OT interventions change over time. My hope is that there will be more evidence-based practice.
Task-based interventions are highly effective for gait and ambulation among patients with chronic CVA and TBI provided that a sufficient intensity is maintained.
In my experience, the Top-Bottom approach is more effective which helps to gain more relaxation, improve blood flow using PNF Technics. and passive mobilization.