It is really important to distinguish between different situations here. It's not applicable to say "sharing is good" or "sharing is bad" because it depends on the situation. There is a wide wide gulf between a classroom situation, where the teacher has willingly signed on to share his/her knowledge and the students are expecting instruction and insight to be conveyed; and the relationship between two professional working artists, where one is trying to shortcut their way to success by copying another.
I was a teacher for 7 years, and I gave it everything I had. I even gave the studio my recipe for my signature glaze. They ended up not using it, because guess what, it did not work for them. This is a good example why sharing something deeply personal won't necessarily hurt you. Like others have mentioned here ... your own experience, studio conditions, personal work habits, etc., are also part of your results. These are things you can't hand over to someone else, even if you try.
Most of my students were not professionals, which is why I didn't mind sharing my design ideas. However, the studio did conduct some "student pottery" sales. Once in a while, a student would take one of my designs, produce it in multiples, and try to sell them. That bothered me, but at the same time I knew no one would confuse their work for mine, so I let it slide.
I also had an advanced class which did contain some bona fide professionals and aspiring professionals. Again I did not mind sharing my ideas with them, because I only accepted students who demonstrated a strong sense of ownership for their own ideas, which means they had respect for others' ideas too.
I taught all of my students to ask first if they wanted to attempt another person's idea, and to accept "no" for an answer. I can't recall anyone ever saying "no." Just being asked first shows respect. I can recall plenty of times when a person copied without asking (usually the copier was not one of my students) and even for a recreational potter, the pain and hurt caused is very real. As well as the notion "maybe a group studio is a bad idea" which is a real shame.
Among working professionals ... when I meet other potters working at the same venues as me, there is a huge and wonderful amount of respect for another potter's styles and ideas. It's easy to share ideas amongst peers like this, because the respect is apparent. This is similar to my advanced students' attitudes, only magnified by many more years of experience. A potter who has made it this far has invested years in their own ideas. We believe so strongly in the path we've taken. Why would we abandon our work for somebody else's ideas?
So when does copying happen between professionals? In my experience, it is when one of them is struggling hard, and does it out of desperation and expedience. THIS IS NEVER OK. I had a bad experience once with an aspiring potter who sought my advice a lot. Over a couple of years, her work drifted towards mine. Sometimes she would get mad at me because she wasn't having the same success. Then she blatantly copied one of my designs. I stopped talking to her altogether, it was not worth the stomach ache.
I learned an important lesson. These days I am not stingy with my information, but I am very selective about who I'll give it to. Just like others have said here ... how someone asks makes a big difference. The attitude matters. Is it respectful and thoughtful, or demanding and entitled? Does the asker seem to think pottery is hard, or pottery is easy?