I recently upgraded to a larger screen, a 30" 2560x1600 Samsung LCD panel. I'm not sure a screen this large is ever "necessary", but our GUI development environment takes up so much space, that my smaller screen was almost unusable. When we work on our WPF screens, we usually have five different panes open, with two main panes sitting side-by-side -- the GUI representation of the screen and the XAML code-behind where we write the screen code.
With my smaller 21" monitor, I could only see ten lines of code at once. With the new monitor, I can easily show the GUI and code-behind next to each other, at least 50 lines at once, making it much easier to debug and add features.
FinFolio follows the same paradigm, letting you put different panes beside each other. If you have a larger monitor, you'll have a richer user experience because you can display more information panes at once. For example, a large monitor may let you display three graphs, and errors/alerts messages. With a small monitor, you may only have room for one graph.
Bigger is better for a FinFolio screen with one exception--on large monitors the relative font size ends up being much smaller. Since I got the new monitor, I've been straining to read text in FinFolio and I often find myself leaning forward to get closer to the screen.
As a solution, we implemented a feature you see in most Microsoft Office products, the lower-right-hand-corner application zoom. It's was easy to implement and it improved my user experience so much that I'll point it out to everybody else:

It's simple to use. Move the slider or click the zoom button to proportionally increase the size of your text, screens, graphics, etc. I find that 110% works best for me. It increases the font size just enough that I'm not leaning into my monitor any more. All of the text renders as vector graphics, so you don't see pixelation or choppy text, even if you zoom it to 400%.

You can also zoom out to fit more on the screen at once:

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Beta Update - We're releasing the beta one week from Monday: 6/8. If you want a head start, download the Alpha 3. It's feature-complete except for the billing module so you can try the Techfi conversion and test the interfaces.