The decision to retract flaps depends upon how much altitude you have below you. If you are at 10,000 AGL then retracting the flaps would make sense.
I have to agree with FI no.1 - but there is a caveat here.
During my flight training I was also drilled into not retracting flap on approach, the pitfall being that you retract flap at a speed which requires it to maintain a buffer against Vs. On approach, you may not have sufficient height to recover.
That said, if you have drag flap out and need to 'stretch' the glide - get rid! But be aware you need the speed first.