Let's imagine that you want to create a texture, which has different areas, related to the specific meshes. For example, sci-fi panels.
If you just randomly create these areas on texture, you will get bad grid snapping and as a result much longer mesh placement, especially for big environments.
How to avoid this? Texture planning!
This texture looks nice, but if you will cut actual mesh into the pieces according to the texture, you will get bad grid snapping.
All textures usually have square dimensions(with some exceptions). Which mean that if you're making a wall, it would be easier for you to cut it into segments, according to the texture, if it also has square dimensions. For example, let's take a wall with dimensions 4x4m. It's really easy to split such texture into the pieces, which have a good grid snapping possibilities. Why? Let's make some simple calculations. Our texture has 2048x2048px resolution. Which give us the possibility to split it into such segments in width:
In this case, you can make a wall with 4m width and 3m height and use only a part of texture for that wall. But in this case, you need to calculate available height, which you can use in texture.
It's easy to do. Just add 1m and 2m heights and you'll get 1536px, which you can use for wall texture. Other 512px you can use for something else.