Modelling for Unity, should I remove intersecting parts? I think, especially when modelling for game engines, using "components" makes production faster and allow reuse of previous models. But this comes with a price: If the designer models (for example) walls and roof seperately, when they try to put them together, inevitably they will intersect with each other (or leave gaps, which leads to same thing).

When the intersecting part is visible, of course it needs to be edited, so it fits in one another.

My question is when the intersecting parts are not visible, does it cause any problems either with unity or with blender to leave them as-is, or should I join them together and remove intersecting parts?
If the pieces are two seperate objects, press Ctrl + J to join them, that is better for performance, because it reduces the drawcalls from 2 to 1. If the pieces are one object with two intersecting pieces, this is fine, in fact, it is better than wasting resources rendering hundreds of faces when you just need 10. Sure, if you zoom in really, really far, the intersection won't look too pretty, but how often do zoom that far in on the roof of a house?