Going by feel and eye is great if you have the ability......but few do.
The more drawings, planning, keeping things flat/square/parallel and using layout lines, the more precise you'll be....and not just one time....its repeatable. So you can get consistent, predictable results.
There will ALWAYS be the need for a critical eye. Sooner or later your layout lines have to get sanded away. The good news is that using repeatable, predictable methods helps you see what symmetry looks like so you can train your eyes at the same time.