When you think about where ideas are generated from, they can come from an individual (single), or from an ensemble (group). Each of these sources has value, and some different characteristics.
An individual idea is generated from the personal experience and framework of one person. Any kind of brainstorming that might be applied to the idea will be within where that one individual’s mind might go — again, subject to an individual’s frame of reference.
An ensemble idea is generated from the personal experiences and frameworks of multiple individuals, and with a group dynamic applied to how those individual points of view come together collectively. A group may come up with ideas that an individual would never have considered because the group participants play off of and complement each other’s personal contributions to reach a collective answer. A group format can be a great incubator for idea generation.
The important thing to watch for is to set up the structure for group interaction to make everybody an equal player. If the mix of individuals in the group idea generation activity includes managers and their subordinates, consider taking the brainstorming session off-site (outside of anybody’s office) and ask for everybody to dress in the same attire (probably casual).
Once the physical aspects of equality are managed, you’re going to hit the hardest aspects to manage — the “mind” aspects. A subordinate is always going to be thinking about how their boss is going to judge what they’ve just said. Consider if you can ask for resources who are not in direct manager – subordinate relationships to be part of the brainstorming — will this still give you the right mix of personal experience and knowledge that can be brought to bear on the problem you’re trying to solve? If yes, then go for it. If no, then you’ve got to drive home ground rules that will ensure the subordinate will feel ok with expressing their opinions and ideas, even though their boss is in the same room. Not easy, but worth the effort if you need their individual contribution to the ensemble result!