TexFix

Minecraft has a cool feature for loading textures, it loads them into ram and then uploads them to the GPU,
what normally would happen after that is if the texture isn't animated mc would get rid of the TextureData from your Ram.
Thanks to forge this isn't a thing any more.    
There comes this mod into play, after everything is loaded it goes over your texture manager and deletes all the none animate sprites from your ram to reduce the amount of Ram that is using.

For vanilla  forge playing that has no real effect.   
But usually modpacks have a lot more textures then usually, I have seen packs with 40k textures. I use that as an end example:    
Vanilla mc has 729 (795 for 1.12) texture in 1.10.2 that are not animated.     
So here is the list of how much that saves:

• 16x Textures = 1KB per Texture = 729KB in Vanilla = 5MB with 5k Textures = 39MB with 40k Textures,
• 32x Textures = 4KB per Texture = 2,8MB in Vanilla = 20MB with 5k Textures = 156MB with 40k Textures,
• 64x Textures = 16KB per Texture = 11MB in Vanilla = 78MB with 5k Textures = 625MB with 40k Textures,
• 128x Textures = 66KB per Texture = 46MB in Vanilla = 312MB with 5k Textures = 2,5GB with 40k Textures,
• 256x Textures = 262KB per Texture = 182MB in Vanilla = 1.2GB with 5k Textures = 10GB with 40k Textures,
• 512x Textures = 1MB per texture = 729MB in Vanilla = 5GB with 5k Textures = 40GB with 40k Textures

This assumes ofcourse that every texture is that spesific size but even if you have a mix inside of that you get a bit of memory saving, since that data is there and does nothing! It is already inside your GPU and its used there.

Also these effects can be greater if Midmapping is used, since mc creates duplicated data to generate these, if you use midmapping then expect a lot more memory being saved. (this is not counted log)

After the Textures are loaded there will be a log of this tool that say: X Amount of textures were fixed and you saved Y amount of MB (Z amount of Bytes)