More #photography nerditry:

My main camera system is what's called "medium format'; the sensor is 40x54mm, which corresponds to the "645" format that used 120-type roll film. This is about 2.5 times the area of the standard "full frame" 24x36mm used in 35mm cameras, but only about 1/5th the area of "large format" 4x5 sheet film.

What's the significance of sensor size? Several things...

The most obvious is that a larger sensor can fit more pixels (assuming a given size pixel element). My sensor has about 150M pixels, each about 3.75 microns. This is roughly the same pixel density as a 60MP "full frame" camera.

If you want more resolution, you have to either make the pixels smaller or make the sensor larger. And we're approaching (and perhaps past) the practical limit for how small sensor pixels can be - resolution is now more limited by lens quality than by pixel density.

A really good (full frame or medium format) modern lens can resolve around 100lp/mm, and that becomes limited by optical diffraction when shooting smaller than about f/8. That's already lower resolution than 3.75 micron pixels can capture. Sensor engineering has basically surpassed what the slower-moving field of optics can deliver.

Also, as you make sensor pixels smaller, they become more susceptible to noise and other issues.

So there's not much room in practice to improve pixel density...

So that leaves sensor size. Making larger sensors is harder, and right now the largest standard still camera sensors produced are the 40x54mm size used in my camera. As a practical matter, if we want more than the 150MP that can deliver, we have to either stitch multiple images together or wait until someone makes a larger sensor with more pixels.

So other than resolution, what are the effects of using a larger sensor?

The first difference is that you need lenses that can project a larger "image circle" to cover the larger sensor. A lens for a 35mm full frame camera needs to project about a 43mm diameter image to cover the whole frame. But a 40x54mm sensor needs a roughly 68mm diameter image. As you might imagine, making lenses with larger image circles introduces new tradeoffs. And we might want an even larger image circle than the sensor requires to allow the use of perspective correcting shift movements.

The other main difference is as sensor size goes up, you need to use a longer focal length lens to achieve the same angle of view across the frame. E.g., to get the angle of view of a 60mm lens on a "full frame" camera, a 40x54mm camera would need a roughly 90mm lens (with a larger image circle).

And as focal length goes up, the depth of field for a given size subject in the frame goes down at the same aperture...

In practice, what this means is that photos made with larger format cameras tend to have shallower depth of field than those made with smaller formats, even though large format lenses tend to have smaller maximum apertures. (My fastest medium format lens is f/4, which would absolutely slow by full frame lens standards).

This is both an advantage and a disadvantage. It's harder to achieve deep depth of field, but easier to highlight subjects with selective focus.