Net pressure option makes difference in calculations for footing loosing contact with soil. For concrete design, if footing self weight is neglected when footing is losing contact with soil, the bearing pressure will be much higher because of reduction in counteracting force for uplift. Soil pressure diagram for ultimate load cases without self weight considered will look like below.

Slope of bearing pressure line is not correct in case of footing loosing contact with soil if self weight is neglected. This approach will lead to extra conservative design as shear and moment values will be much higher.

If full self weight is considered for concrete design, then soil pressure diagram for ultimate load cases without self weight considered will look like below.

In most cases footing will be in touch with soil because of factored self weight and axial weight stabilizing the footing, but maximum bearing pressure resulting from this approach QMAX will be still on higher side.

IF net pressure option is considered then effect of self weight is deducted from pressure including self weight.