The platform could proof to be very important. An adult, healthy newt in an stablished, fully cycled, heavily planted tank is VERY unlikely to ever come out of the water. However, there are situations in which the newt may need to, and if unable to, it could potentially drown.
If the tank is not fully cycled, then fluctuations in water quality may force the animal to leave the water, even if it´s just for a short time. High temps have even a stronger effect. If temps get too high, a newt may become terrestrial (this is a natural response to the problem in nature). A terrestrial newt will desperately seek to get out of the water as its internal physiology changes. If unable to scape the water, it can drown. I´m not saying it will, but it can definitely happen.
Consider the platform a safety net. If something should go wrong, the animal will use it to scape the inadequate conditions, or simply just to rest for a little while (this may happen specially at night).
Since you are still in the process of learning and adjusting your care for the newts, i´d recommend, like Jen has, to provide a platform, just in case. Once completely settled, and once everything is exactly as it should be, then it will become pretty redundant and unnecessary, and possibly completely unused, although it´s still never a bad idea to provide just a small above water surface.