Let's get practical. You ask the question on here as to what you can do, or not. If in doubt ask ATC not prune. You are cleared, on HDG, to 4000' and cleared approach. This would suggest you are cleared to intercept the final track and descend on the procedure from 4000'. If you feel you will intercept the final track too close for 4000', i.e. be above the profile, you would ask ATC for further descent. If 4000' is OK for the distance at intercept there is no problem. It is not uncommon for ATC to forget to give you further descent, but is it necessary? Remember the PIC is responsible for navigating the a/c to a safe approach to landing. ATC is responsible for terrain clearance, but PIC has final responsibility for managing the energy and safety of their a/c. Situational awareness is the crew's responsibility. ATC can screw up as easily as you.