If the blocks above are 12 inches square, the sashing is 1 inch wide.
Often considered a little small it looks OK to me, and would be best with identical blocks.
I would use this more as part of the overall design rather than as something to keep the blocks separate.
If all the blocks were different I think I would like to separate them more than this.
Double the width, and it still looks OK to me.
The sashing is now a feature in its own right.
I would use this width to separate similar, but not identical, applique blocks.
Now we are up to 3 inch wide sashing between 12 inch square blocks.
I still like it, but it is fairly unlikely I would choose to use it between identical blocks, though I rather like it between these Nine Patch blocks.
However, if I had a collection of very different pieced blocks to put together as a sampler quilt this would probably be my choice.
I am about to start a new series of virtual designs with a focus on sashing, so don’t go too far away!