With a low powered aeroplane, you need armfuls of power for a small speed change with full flap selected (thinking C152 in particular) which can destabilise the approach quite significantly potentially requiring a lot of trimming. This isn't particularly desirable when you're first starting out which is why elevator=speed, power=RoD is generally taught. I'm not especially familiar with the PA28 so it may be that it's less of an issue with this type. The best suggestion: ask your instructor.
However, once you move onto something a bit more sporty.....