To unwrap interferograms on a desktop or laptop with Snaphu, you want to keep the width of the tiles less than about 3000 pixels or you will run out of memory. You can unwrap the whole interferogram as one if it is narrower than that.
More tiles increases the chances of mismatch between tiles.
The tile overlap should be around 200 pixels. I don’t know why the default in SNAP is 0. Snaphu needs some overlap to match the phase between tiles.
I don’t know what the tile cost threshold is.