The simulator is a wonderful learning tool.

G3/G4 does a great job at simulating an RC plane, and it does so with great fidelity.

However no sim will subject you to what you'll experience at your airfield.

Bugs, the sun getting into your view, other planes, unexpected wind motion over the ground, other pilots, etc.

Couple that with the knocking knees you'll get on your first flights, and you'll find that your experience at the field is unlike what the sim gives you.

That said, the Nexstar and PT-40 in the sim really do mimic the real planes quite well...

So much so that my 10 year old daughter's first attempt with an Alpha 40 ( which is identical to the PT-40 ), went quite well thanks to the sim.

Needless to say the sim does not teach you the nuances of setting up your plane. Nor does it help you spot problems, tune your engine, nor get you prepared...

You NEED an instructor for all of that.

The sim will not eliminate the need for an instructor, but it will greatly reduce the amount of time you have to spend learning, before you certify.