Object face validity When creating objects for a game engine (unity) or in general I often come across a choice. I can make a face of my object be the way on the left or join the faces and have them as such on the right. Is the way on the right valid? Does it lead to any errors?

If it is wrong, why is it wrong and what are the consequences?

This is more of a modelling question, not specific to blender.
An n-gon like the one on the right will be transformed into triangles (triangulation) by Unity, and that triangulation is unpredictable. The insets might be covered by stray triangles, for example.

In general, any topology with concave polygons is problematic, because you don't know how it will be triangulated. Convex polygons, in the worst case, will only give shading artifacts.