You guys both missed my "or rated pilot" though. You're correct on a true pre-solo Student pilot.
Commercial rating instruction, may be a good example. If the CFI takes the controls to demonstrate a Chandelle or Lazy Eight, shouldn't the PIC time logged by the "student" be a couple tenths less than the CFI for the flight? Two pilots are not required when the CFI is demonstrating (unlike when a "student" is under the hood working on an IR).
Lots of people make a big deal about this for an Instrument pilot using a Safety Pilot for currency, with one agreed to act as PIC and the other required due to the view limiting device, but every logbook I've seen (granted not many) of a Commercial candidate and their CFI -- match minute for minute the PIC time to the tenth, during the hours leading up to the Commercial rating.
Same thing if an IR "student" is flying under real IMC with their instructor who filed for them. Instructor has the controls, "student" has to stop logging for those minutes, technically... there's only one PIC needed at that point.
I know it's not a lot of time, typically, but it's at least as much time as that VFR to "hooded" transition for a Pilot and Safety Pilot combo that even DPEs make a big deal about not having the same numbers written in the logbook.
Interesting point, while I have seen where pilot/safety pilot pairs have been busted for identical logging, I have not heard of the same result from instructional flights being double logged identically. My guess is this relates to the instructor not Acting as PIC either, rather as in Instructor, same reason a CFI doesn't need a valid medical for teaching rated and current students. What I don't agree with is allowing the CFI PIC time with a rated and current student.