Negative LOD bias?

[TheRyuu]

It's the last option in the Per. and Quality settings.

Should I have it on allow or clamp?
(and what is it?)

 

[xtknight]

Stands for Level of Detail, and lower values will make textures more grainy. Just leave it on allow, as some games might need access to it.

 

[Ackmed]

Clamp helps with shimmering, if you notice it.

 

[BFG10K]

Clamp it because you should be using AF anyway.