usually nothing,but you should be careful because when you use Transient Simulation
in OrCad or other simulation softwares and you use mixed circuits like opamps, you
may see convergence Error.Because the solvers of these software usually solve
equation at minimum time step,this means your time step is too small because
usually you have a little R*C in your circuit.this may be caused by OPAMP or any
other mix model.in this case you should use resistors with your sources or