Where do new ideas come from? The answer is simple: differences. While there are many theories of creativity, the only tenet they all share is that creativity comes from unlikely juxtapositions. The best way to maximize differences is to mix ages, cultures, and disciplines. — Nicholas Negroponte
Same people, who live in a same context, have the same hobbies often have the same type of ideas. So if you are planning to generate ideas only with people like you, for me that would be white christian males, you won't go that far. As Nicholas says it in the quote above, new ideas come from differences.
So it's good to have people from different ages, cultures, disciplines, genders, and so on. In a business context I would highly recommend that you don't generate ideas only with people from your department. Get some people from the other departments, especially get some people who work at the front office. Even better, bring a few of your customers in the ideation session. This will add a lot of diversity that will bring a lot of different ideas.
It's great to have a lot of ideas, but if they are all the same it defeats the purpose. That's why we are looking for different ideas. And to come up with different ideas we need different brains.