Procedural Assignment

I have a few fundamental questions to ask:

Question:

1. When writing test bench, are the combinational and sequential logic important?

2. From the attachment, why this assignment (a <=# 5 b)is under comb logic? at the same time, why this assignment (q <=# 5 d)is under seq logic? Shouldn't be the same?

3. Why inertial and transport delay are under comb logic? there is no inertial and transport delay in seq logic?

thanks