If you have an object larger than a tile, you could alternatively import this image separately to avoid it being cut into pieces, making placement easier. This would be commonly done for semi-large objects like trees and bushes.
When it comes to houses, it is quite common to build them up from smaller pieces to allow for variations in size, room layout and small visual details. In this case, it is not possible to have those pieces align on the tileset since their graphics would overlap, which would stand in the way of using the tiles in any flexible way.
That said, there is a use-case for cutting actual isometric or hexagonal tiles from a tileset image. The approach would work for ground textures as well as small and large objects that do not require other objects to go behind them (though even in this case, sometimes another layer could be used to facilitate that). And indeed, it would make both the development of the tileset as well as the use of the tileset much more comfortable. So eventually, this is something I’d like to support.
This approach usually works, and certainly works for the standard isometric map. For staggered maps though, copying regions is currently not staggering-aware and as such any multi-tile object will get messed up when moved by odd distances along the staggering axis.