Someone asked me this yesterday. This wasn't about saying “No Comment”  but rather about being quoted on a situation about their industry but  not directly related to their organisation.

 There maybe lots of good reasons to stay silent, but one simple question to ask is  whether anyone will miss you (your organisation’s voice) if you don't provide a comment.

 Plenty of reporters will call for comment on issues or events that are tangential to your business. If the story is not about your organisation, stay out of it unless you have a clear message that you know will make it into the story and you are comfortable that the story won't turn into something you don't want to be part of. 

Here are some other reasons by Ragan contributor Jim Cameron

1) When you have history with a reporter / publication that misquotes you and always gets the story wrong.

2)When you are asked for confidential, proprietary or personal info not relevant to the topic. 

3) When you don't have a message and therefore end up in what feels like a deposition.

Are there any other reasons I have missed?