I'm starting to build my pitch deck and need more detail as we're launching a private photo messaging app.
Great question - to build also on Tom's response, I would say that the TAM for entrepreneurs who are building pitch decks is the start down the path of what I like to call "CEO math" - starting with TAM, while making logical sense, is really a means for lazy calculations on projecting market growth and even in crafting your go-to-market strategy. This is where people fall into the all too common "we will just get 1% of the market...." pitch; and that is a soundbyte that few if any serious investors will be welcoming.
It's an OK data point to quick reference, but if you are taking in terms of building out a market growth model and/or projecting finances based on assumed downloads, traction, MAUs etc, I would hyper-fractionalize your markets and go after a very narrow and specific segment (it's better to get 99% of a grape than 1 % of a watermelon.) Investors tend to respond more positively and can more easily wrap their minds around your model and plan if you show are you aiming down the sights a bit rather than shooting from the hip.
I'd be happy to help walk through data points, how to find them, and how to present them to potential investors in your deck. Feel free to request a call and we can go from there!