Inclusive quasielastic and inelastic scattering from nuclei and nuclear matter is analyzed within the plane wave impulse approximation. Theoretical results obtained using model spectral functions including the effects from nucleon-nucleon correlations are presented and compared with results obtained with realistic many-body model spectral functions for $^{3}\mathrm{He}$ and nuclear matter. The sensitivity of quasielastic and inelastic nuclear structure functions to different prescriptions for the off-shell behavior of nucleons is investigated in both the x1 and x>1 kinematic regions. Results indicate that the inelastic scattering in the x>1 region will only be important at momentum transfers above 8 (GeV/c${)}^{2}$.