Imagine that you have an image with a small sample of a texture. If you want to generate a larger texture with this small image, you could just copy-paste it, and put the copies (or "patches") one next to another, but that wouldn't produce a very good result, since the right (or top) part of the image usually doesn't correspond to its left (or bottom) part, when two copies of the image are assembled.
A few images are indeed designed to be copy-pasted one next to another and still look natural, but the result is usually periodic and very monotonous (it looks like wallpaper -- the one on your walls, not the one on your computer desktop!).
Texturize lets you actually create tileable textures (which is great for game design).
I have a LONG history with Blender - I wrote some of the earliest Blender tutorials, worked for Not a Number and helped run the crowdfunding campaign that open sourced Blender (the first one on the internet!). I founded BlenderNation in 2006 and have been editing it every single day since then ;-) I also run the Blender Artists forum and I'm Head of Community at Sketchfab.