We wouldn’t dial in an altitude lower than ATC has cleared us to even when using VNAV and even when there’s an altitude restriction in the legs page. With ADS-B, ATC can see what you have selected on the MCP. They want to see the levels, waypoints or headings that they’ve cleared you to and they’ll usually get your attention if you’ve selected an incorrect value.
If ATC clears us to an altitude lower than the restriction on a point ahead of us we’ll still select on the MCP the level that ATC has cleared us to. We usually know if they still want us to respect that altitude restriction. If we’re not sure we may ask “are we still required FLXXX at point YYY?”. They may say yes or they may give us unrestricted descent. Sometimes they’re specific with descent clearances and they may say “Descend FL150, cross point XXX at FL190 or below”. Or “descend FL190 to be level by point XXX” or “Descend FL150 at 1500fpm or more”.
During the last portions of descent we may be cleared for approach when there are still a few altitude restrictions ahead. In this case, the “cleared for approach” part of the clearance means that we must follow both lateral and vertical path as per the chart. In our airline we will select on the MCP the level we’re required to respect on the point ahead of us. So if the point ahead has 5000A, we will select 5000 on the MCP. If after that point there’s a FAF at 3000ft, we will usualy wait until we’re 1nm from the point restricting us to 5000A, and there we will select 3000 on the MCP to continue descending. We’ll do it like that until we reach final approach vertical guidance (after the FAP/FAF) on ILS and NPA approaches where in most cases the vertical guidance will be geometrical. On NPAs, 2nm before the FAF we will select on the MCP the minimums rounded up and shoot the approach in VNAV PTH with SPD INTV and then generally at 1000ft AAL we’ll select the missed approach altitude.