In video games assets are ideally only drawn/rendered when they're on the screen. Sometimes games are poorly optimised, or too demanding for hardware, and you get asset pop-in, where objects will appear out of thin air when you're in range of them rendering. Simple and common example: npcs in sandbox games. They only actually render when they're close enough to the player, even if you can see for miles. It's necessary to prevent the framerate tanking.
Warriors 3 has such atrocious pop-in optimisation that enemies will render in and out of existence even in the middle of a fight. You can be right in the thick of a big group and the edges will disappear/appear as you rotate the camera, even if they're still technically on screen and close. You can run towards a mob of X size, only to find them tripple in size when you're in fighting range. I've been trampled by horseback units in their charging animation because the game didn't render them until they were literally one foot in front of me. A battalion of horseback soldiers appearing out of thin air on top of you.
I'm pretty tolerant of framerate and graphical oddities as long as shit still works and is consistent. Warriors 3's pop-in is so bad it actively hurts the game's design. Low standards will tolerate it, but I think the port is horrible and not worth support.