This started out sensible; you can't get insurance coverage to go solo in that helicopter or twin so your CFI rides along to make this operation legal. Hypothetically, there is no assistance rendered and the "PIC" is entirely the "solo student" (no helping or hinting). Then this morphed into single engine aircraft like a Piper Arrow and as examiners we start to wonder what level of solo compentence is actually present. Has this potential commercial pilot ever been alone in an aircraft, possibly scared and entirely on their own? Without this level of courage and self-efficacy there is something missing in our future pilot.Here is an FAA interpretation from a helicopter school and some other reference material. John Lynch added some context back in the day (no longer regulatory but valuable for FAA original intention). The key for examiners is to make sure the time was correctly logged as 61.129 time (assisted PIC), and then it can count in a checkride.