But in the Borderlands style you can add some crasy item,
without it sticking out weirdly.

Lets say a clown on a tricycle pulled by rats.
Or a giant P standing for no reason on the steet.

It would not work in Crysis or Skyrim for example.

The more a game relies on (visual) realism, the more it will
throw the player out of his immersion in the world.

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stylized graphics have the advantage to work with less
detail and thus less chance to land in the uncanny valley
when there is an error compared to its real world representation.
Once the rules for the style are set (an followed) the
workload reduces a lot.

For example making a character texture in Minecraft is
possible even for non-artits without much hassle or experience.
Doing that for a Mod in Skyrim would look off in 99%
of the cases. Only a skilled artist can pull that off,
keeping the visual style of the game.