Well, if you are a good speaker and you can show passion when vlogging and reach into peoples hearts / minds I would say it's a way better method to deal with. It's simple, it saves time for people if you are covering a big topic since they don't have to read it, especially if something is really complicated to understand. You can explain that over vlog much easier, be it by gestures, or whatever method, but in general, it makes life easier.