Yes, op, It is as you suspect. There is like this image of 3D modelling from pop-culture movies etc since the 70's and forward that put this idea of like calculating the volume from a righ/front type view of a object.
Almost everyone have seen some version of that so that is what they naively will attempt when starting out (I did the same back in the 90's). As you gain experience you will completely discard such antics.
People teaching you too attempt to model like this are probably not very accomplished at all in what they do. There is several reasons while this strategy will fail, here's the main ones:
When you draw something it's never an orthographic projection of what you intend, because a correct orthographic projection of what you wanna do will look so retarded that you cant really imagine it and draw it out.
We are used to looking at stuff in perspective because that is how we see the real world.
All experienced modelers and sculptors will work mainly from perspective reference, move around the freely and make correction to shapes to ensure they have the same look and feel as the concept.
Not attempt to draw a front/side orthographic projection of a design and attempt to trace it into existence as if being a human copying machine. Just doesn't work out well going that route.
It's a type of training wheels that only serves to limit your development.
The only real use for image planes is establishing the outline of an object of which you have a true orthographic projection, such as the 'blue print' of a vehicle.
Even then most of your work capturing said vehicle will be done in perspective from perspective reference.