Question: In what particular situation you will need a depth knowledge of math/physics in software engineering?

Answer: 
To answer your question: you will need good maths and physics if you are writing scientific (well, physics-type scientific) and engineering programs. For more general purposes good maths is better than bad maths but bad maths is often enough and physics may be totally irrelevant. Good maths is a question of topic (eg graph theory more useful than real analysis, arithmetic more useful than topology) and depth of knowledge.
I'm a Game developer and frankly I must say that you don't need a lot of math and very little physics. All I used so far are Trigonometry,Linear Algebra (for 3d matrices) and some interpolations. I woudn't really say that's complicated math. As for physics some knowledge about mechanics and forces should help if you want to simulate the environment but otherwise I woudn't really see the point.  

I also did some other applications in my spare time never needed any math that's over 8th grade.