Today we're not just talking about branding but, in particular, YOUR brand. The first thing that our brains do, when coming across something new, is to classify it along with something else, something familiar. This means that we stereotype - everything.
Therefore, knowing how people are most likely to stereotype you allows you to determine what works for your brand... and what doesn't. This allows you to develop strategies for playing into and building upon this impression or to break that pattern of thinking immediately so they are forced to re-classify you!
Although it may not be politically correct in today's world to speak about stereotypes it doesn't mean they don't exist. Spending time to understand how you are most likely to be stereotyped allows you to find ways to capitalize on or to shift those impressions - ensuring always that they help to sell your desired branded message.