You can, but it’s not recommended because it’s very inefficient. Usually you create base classes in C++ and do all your functionality there, but it makes sense to create Blueprinted sub-classes that might change some of the initial properties, such as the mesh used by a Character etc.
ShooterGame is a good example of this. All code is written in C++ and handled by that, but discrete objects sub-classed to Blueprints which just alter some of the default values. This allows the same players to have identical functionality, but with different meshes, inventories, health values etc. The engine is built and designed to be used like this.
Remember, you’re most valuable commodity as a developer is your time! Blueprint is so scary fast that it cuts a lot of that time out!
Blueprint itself IMO, is worth ten times the price of the engine on it’s own. For prototyping it’s second-to-none.