Do you use a business plan?

Hello everyone. I'm here today because I'm trying to create a business from the ground up and I believe my next step is to create a business plan. My question to successful entrepreneurs is this: do you have a business plan for your company? Is it used strategically or is it created just for financial purposes? And finally, do you have any recommendations on how you created your business plan (i.e. resources to use our sections to include)? I'm trying to figure out how seriously I should delve into each section. Thank you for your time!