I like how easy it is for people outside any one department or team member can easily communicate ideas across departments as well as within teams! It's also great when all members are in agreement about an idea (which happens fairly often).
Sometimes there isn't much feedback after submitting so you don’t know if anyone else has seen/considered yours yet but this seems rarer than what would be expected from such large organisations - maybe because we're small? We've had some very useful discussions through brainstorming via IdeaBank which have led directly into projects being implemented by our clients.