This was the cause of the signature jiggly textures that were pervasive in PS1 games
The real issue is that the PS1 has no subpixel precision. In other words, it will round a triangle coordinates to the nearest integers.
Likely the reason why they did this is because then you can completely avoid any division and multiplication hardware, with integer start and end coordinates line rasterization can be done completely with addition and comparisons.
https://all-things-andy-gavin.com/2011/02/04/making-crash-ba...