Suppose you are in VNAV PTH descent and are approaching the IAF for your Approach, The IAF has both an altitude crossing restriction and a speed restriction. Assume that your VNAV PTH descent is at 240 kt at that moment and the speed restriction is 210 kt.
Will VNAV automatically "see" the speed restriction and reduce the descent rate (pitch up) to meet the lower speed? If yes, won't it then miss the altitude crossing restriction, as the planned path is modified?
If the PIC uses SPD INTV to set the limiting speed, won't VNAV switch to VNAV SPD and thus once again automatically pitch up to reduce the speed? Again, this may result in not meeting the altitude restriction, as you will end up higher than your intended path.
So, the question is, what should you do in a situation like this? My guess is, revert to V/S and MCP SPD, use Speed Brakes and arrange to be over the IAF at the correct speed and altitude, and then re-engage VNAV.