This mod is a library that's required by some mods (ArchaicFix, NotFine, and Hodgepodge are some examples.)

Oh. The main features are:

• The ability to safely use Mixin without having to embed it in your jar
• The ability to mix into the classes of mods that are not coremods using late mixins, which are mixins that get loaded after Forge has put all mods on the class path.
• MixinExtras adds some injectors, see its wiki

I mean in mod development with mixins

Ok, thanks