Modeling (initial conditions)
Initial conditions (ICS, steady/unsteady flows)
ICs should not affect final results and only affect convergence path, i.e. number of iterations (steady) or time steps (unsteady) need to reach converged solutions.
More reasonable guess can speed up the convergence
For complicated unsteady flow problems, CFD codes are usually run in the steady mode for a few iterations for getting a better initial conditions