I have mentored for SCORE which is small business advising and is pretty old school, but they no longer push for business plans unless the client is looking for a bank loan.

Instead, the choice of a lean business plan (business model canvas) is also offered or at least talked through. Someone has an idea but isn't sure what to do next. Well a business plan can just be the very essentials (who do you plan to serve and how... what are you planning on actually doing and can you afford to do that)