What's the intent behind what you're producing? Why do you want write a business plan / pitch deck? What are you trying to communicate and to whom?
The answers will affect what you produce.
For example if you're looking for bank loans for you business, or approaching investors, they'll often want to see something moderately formal at some point (especially the banks). There you'll probably need a business plan.
If you're trying to grab an investors initial interest then you need a good solid pitch deck. You need to be able to communicate your business ideas clearly and concisely. However they are primarily a sales tool - so using them as your primary in-house mechanism for understanding your business can lead you to overlook some of the risks.
If you're trying to understand your own business model and see where the gaps and opportunities are I personally find tools like the Business Model Canvas much more useful. They're far more rapid and flexible than the normal N page business plan, and I'm less likely to delude myself than I am with a pitch deck.
For example we've been running successfully for a couple of years without any sort of business plan. We do have a Business Model Canvas that we evolve and tweak on a regular basis (e.g. we've currently gone through quite a major change from production to education in the work we do with clients). We also have the usual in-house cash flow forecasts and some short, medium and long term goals. And that's enough for us. Since we're bootstrapped money wise and aren't looking for external funding or loans producing a formal business plan would be a waste of time and energy. Since we're not looking for investors a polished pitch deck would equally be a waste of time.