Personal branding is more useful for people who are far from the stereotype for their group.
Personal branding (twitter, blog, etc) gives people extra information to extrapolate who you are from. It is more useful when people’s prior of who you are is far from who you actually are.
For example, suppose you are a part of group X for which property Y (being in tech, knowing math, being analytical) is (thought to be) rare. Networking with strangers is hard to do. They will likely give you dumbed down explanations and underestimate your aptitude, so you will have to waste time proving to them that you are an outlier for your group.
If, on the other hand, people can form a more calibrated model of you from your “personal brand”/online presence before meeting you in person, then you no longer have to waste all that upfront time.