A logo is a must, it needs to be distinctive and gives a consistency to the product, which is ultimately you and your business. if promoting things , everyone likes to see a face behind the marketing, its the now like and trust things, you know, if you want me to look at your product I need to know who you are. however sometimes it is not necessary and can often come across as a bit of a shallow sell. eg: you dont see the owners faces on Steem Promotions, but you do see the Logo, which is dynamic and recognisable, however you can always find out about the faces behind steem if you look deeper