Yes, although it can depend on who you’re speaking to and how you’re trying to secure funding.
If you’re trying to get a loan from a bank, a business plan is almost mandatory. A small business loan officer will evaluate the validity of your plan and may come back to you with questions before authorizing your loan.
On the other hand, a VC firm or an angel investor may expect a pitch, rather than a business plan, especially if you’re in a pre-seed round and have no cash flow or financials that they can actively evaluate. They’ll also be interested in anything else you can use to make your case, like intellectual property (patents, inventions, etc.) that make your business model unique and defensible.
In either case, your potential investors want to know that you’ve done your research and that they aren’t throwing away their investment. Even if you need to pitch, starting with a business plan can help you figure out how to address these pressing questions.