You should fly as your instructor "instructs" you to fly. Whereas the flight manual will include recommended flap settings there may be other operational considerations, as someone pointed out above already, perhaps a short runway, or high obstacles on approach?
Landing a C152 flapless will require a fair bit of nose-up trim, so maybe your instructor doesn't want you to do this solo yet for fear of you having a low speed premature take-off and consequent low level stall?
Funnily enough in my last flying group, the ops manual encouraged the use of landing and take-off flap at all times on their high wing Cesna's just to minimise ground roll and thus tyre wear. It was also prohibited to use full flap because they kept getting stuck down. Which is a real problem if landing away somewhere where there isn't an onsite maintenance facility as you can imagine!
When you take your skills test though the examiner is going to ask you to demonstrate circuits in varying configurations so you will need to be able to land with various flap settings as well as flapless.