It's pretty simple:

• Better block culling
• Stop rendering faces that cannot be seen anyway
• Fix some model related bugs

All without changing how the game looks(assuming you cannot look through walls and ignore the third point for a sec as that makes some small changes) at all!

Tbh it doesn't make a big difference in performance(if that's what you're looking for) but it's better than nothing.

Q & A:

• Q: Is this compatible with *insert any other resource pack or mod*?

• A: It should be fully compatible with all other texture resources however in some cases the optimizations may not work correctly.

• Q: Can my low end pc run this?

• A: If your pc can handle minecraft in the first place it can most definately run this!

Found a bug or have a suggestion?
Report it on the issue tracker or fork the project and open a pull request!