*with apologies to George Clinton
Someone up the chain of command recognized a problem, or a competitor is eating your lunch technologically and you have to catch up, or an executive read about some boffo new technology in an in-flight magazine and wants one of his own. In any case, they slapped the "project" label on it, and now it's your problem. You have, if you're lucky, a sketchy list of things it needs to do, a timeline, maybe a budget. Problem is, no one really seems to know what this thing will look like when it's done, or what it must and must not do. You keep having conversations like "well, we've always..." or, "can we < insert incredibly-detailed spec > ". You need scope, and you need it fast.
Mind Mapping isn't in the BABOK and isn't a part of the standard BA toolkit. But it's a helpful way to jumpstart a project and it can help your team to begin to visualize the end product. And after project initiation, mind mapping can help you choreograph the complex dance among artifacts as you proceed through requirements gathering.