Any tips regarding Modular Geometry?

Hey guys I have been working on a few projects lately but I want to start getting into Modular Geometry modeling. I heard it is a great and effective way to build your levels mostly in games but I believe it applies to many areas as well. I’m looking for tips anyone can give me before I dive straight into this area. I read some things regarding your models to have proper scale and such so its tile-able which I’m assuming is about using the grid and snapping to the major white lines that make up the blender unit.

I want to build modular pieces so I can make a house for example, that might be my first little project and then move to things like making certain flooring pieces for the ground or terrain thats modular perhaps.

So does anyone have any tips on this subject and also can someone explain how the blender units work and is it important when I bring it to unity?