Graduate schools in North America usually have a required number of courses that you need to pass. Afterwards, the school is usually pretty flexible at the student taking more courses (and it is often free of charge), but it is another story with advisor/PI/supervisor.
After I passed my courses, I have been either explicitly or implicitly reminded by my advisor that I should not take more courses. None of any other graduate students are taking courses either in some sort of tacit acknowledgement. Taking courses takes away time from research and performing badly could cause serious problems, so it is understandable.
However, I find that after a year or two of not taking any courses, I feel less mentally "sharp". And sometimes I say to myself "I wish I had taken information theory/blackhole physics/statistical methods!" because I think they could open up more research ideas and plus some subjects are just hard when studied on your own. Finally, taking courses open up more employment opportunities, either through TAship or working in industry. I get the feeling that some/many advisors in academia (such as mine) are fairly indifferent about transitioning from graduate school to industry and do not appreciate the importance of courses/technical skills to these future opportunities.
Has anyone been able to successfully navigate through this dilemma? There are pro and con to each side of the argument and I could't make a move in fear of jeopardizing my relationship with my advisor.