It is always a bit of a hassle to make your litematica selection and in the end your .litematic only the size of the actual building, so that you don't create unnecessarily big .litematic files

Very helpful would be a checkbox to automatically crop a schematic to its minimum size on saving it, just like with ignoring entities.

I know this is a very QOL of life request and I wanted to thank you for all the hard work you are doing on these mods! :)

I don't really like the idea of "secretly" changing the area selection while saving (if it would not affect the actual selection but a separate copy used for saving the schematic), nor would I want the mod to modify the actual area selection on its own while saving.

To me it sounds like maybe you are creating the selection the "simple/stupid way" by flying to the opposite corners of the area and using "Set to Player"? Or how are you creating it if it's so much bigger than the actual build? Also if you have multiple buildings, then you should be using the "Normal"/Multi-Region selection mode and multiple sub-region boxes around the buildings, to avoid making one massive box around everything. There is no way to "crop useless stuff" such as empty space between buildings if there is just one selection box. The Schematic can only store rectangular boxes/cuboids, not arbitrary shapes.

In general the Expand corners mode (instead of the Corners mode) is very useful for properly selecting stuff. You can cycle between them with Ctrl + M or change it in the Area Editor menu. In the Expand mode you right click to reset/collapse the selection box to the clicked point, and then you left click to expand it around all the points you click. So you can always click the furthest block on any side of any build, and you don't need annoying temporary blocks in the corners, or trying to fly to the approximate corners with your player to use Set Here.

And there are also two hotkeys, selectionGrow and selectionShrink that can be used to auto-grow or auto-shrink a selection so that it covers the entire build and nothing extra. These both work with the principle of expanding or shrinking the selection by one block in all directions, and then checking if that new expansion "layer" has any non-air blocks, and if it does, then that expansion is kept and the iteration continues. So the auto-grow will not work if your building is on/touching the ground, as then it will just grow around all the loaded chunks on your client. (But now that I mentioned it, maybe I could add per-direction coordinate locking and make the shrink and grow feature ignore the sides that are locked...)