The Material Strength is used in two places.

It is used by the button Derive from section moduli and material strength to calculate the Max Bending Moment vs Horizontal/Vertical:

It is also used is when checking the results from the Finite Element Analysis (FEA) engine.

Note the Material Strength does not impact on any of the FEA calculations, it is simply used to check if the stress calculated during FEA exceeded the specified material strength.

This check is the Normal Stress Utilization check as shown below for some FEA results.