Generally speaking, my rule of thumb is that an NDA shouldn't be necessary if you're simply discussing the business. If an idea is so copyable that simply repeating aloud it is dangerous, then you're going to get copied by bigger players as soon as the viability of the idea has been demonstrated. So the company's pretty much hosed anyway. When it comes to basic business and marketing advice, it really limits the valuable input that can be gained if the business owners are super cagey about talking about their ideas.
On the other hand, if actual core IP (like code and business documents) is going to be seen in detail and contributed to by someone, then an NDA is a must. Not only an NDA, but also an IP assignment agreement. It must be unambiguously clear that the business, not any individuals, owns the IP of the company. I don't care if someone just wants to help out of the goodness of their heart; if they're looking at the code, they need to be willing to sign some paperwork.
Related: It's incredibly galling when someone wants you to sign an NDA to talk about something on which they have a bullshit patent. Really?? Trade secret XOR patent, please choose.
I get the feeling that companies don't like to talk about or advertise the patents that they own, because it's fantastic for them if somebody else independently has the brilliant idea of rounded corners on the casing of a portable screen.
> On the other hand, if actual core IP (like code and business documents) is going to be seen in detail
This is what I always look for in an NDA or I don't sign one. People generally take some generic NDA contract they found online that is so vague you're probably in violation the minute you sign it. I'm guessing this is why others say it's hard to enforce, so why sign one?
Bottom line: unless an entity has specific IP and other trade secrets they want to protect and it is spelled out in the agreement then I'm not signing it, and if it's required I'm not interested. It's probably a good filter IMO.
On the other hand, if actual core IP (like code and business documents) is going to be seen in detail and contributed to by someone, then an NDA is a must. Not only an NDA, but also an IP assignment agreement. It must be unambiguously clear that the business, not any individuals, owns the IP of the company. I don't care if someone just wants to help out of the goodness of their heart; if they're looking at the code, they need to be willing to sign some paperwork.