If the full ILS is available, on glideslope, then fixes inside the FAF aren't applicable for step-down limitations (particularly where marked LOC ONLY). Outside the GSIA, however, step-down fixes are mandatory, even when following the glideslope (the long ILS arrivals into LAX are good examples).
Regardless of whether one is on the glidesoope or not, however, one should note the altitudes and check them off while passing those fixes. It's good practice to be as situationally aware as possible, and step-downs with altitudes are useful tools for monitoring the arrival and approach, even when following the electronic glideslope. This is especially true in mountainous terrain.