Visualizing electromagnetism is really hard/impossible almost
Maybe electrodynamics, to an extent, but I can visualize pretty much everything in electrostatics. That doesn't mean I will try to visualize everything in some complicated calculation. Visualization is important mainly for understanding concepts, rather than doing the problems. With problems, sometimes there will be a visual inspiration, sometimes not. Depends on the problem. Some are more purely computational.
I strongly disagree with whoever said that trying to visualize in physics is "useless." It's what separates physics from math. Heck, even in math, visualization is key to understanding and retaining it better.
Actually, I am a mathematician, and I think visualization is actually more important in pure math. That is where a great deal of my inspiration comes from in
writing proofs. But you are very right to point out the idea of retaining stuff better. You are trying to learn and take something away from it, not just get a grade on a test and then move on. If you want something that will stick with you, it's usually the visualizations and physical intuition.
Physics is not all about the equations. You can be a master in deriving and manipulating the equations and call yourself good at physics, but if you can't visualize the physics idea behind at all, what's the point?
I don't know how effective one can be at physics if one just manipulates equations (I would see it as a rather severe limitation in certain topics, though). However, I am not interested in that kind of physics. If you are in it for fun, as I am, the whole POINT may be to visualize things. I wouldn't be interested in it, otherwise. Happily, that's less of a limitation than you might think. Einstein talked repeatedly about how he thought in pictures. My goal is to produce conceptual understanding, rather than just answers.
And to your statement that physics intuition can lead you astray, I agree, but that's why you discard your incorrect intuitive ideas and develop new ones. How do you do that? By visualizing the physics, not by staring at the equations.
Exactly. A lot of people like to talk about how pictures can mislead you, but so can equations and calculations. Doesn't everyone make mistakes in calculations, too? It's not that you have to be careful just with pictures. You have to be careful, full stop. Pictures are no different than anything else. Also, people who are very good at visual thinking will not make as many mistakes. I am an extreme visual thinker, but I think it is very very rare that my visualizations have mislead me. Much more accurate than calculation, actually. I can hardly calculate two lines without getting minus signs in the wrong place, etc. But my conceptual thinking is usually dead on.