Ask HN: Is technology evangelism really helpful for the companies?

These days I see lots and lots of tech evangelists particularly from companies like Microsoft, AWS etc. What is general opinion among HNers about this new trend of tech evangelists. To me they are all words, no substance. I am very much skeptical about their impact and ability to promote product and technology for the company - or may be that's just me. Recently I went to a Microsoft workshop, most of technical sessions were simply overshadowed by one technology evangelist, in fact he hacked away the whole workshop. No one from technical team was able to speak out about their experience as this guys was popping every here and there. I was very annoyed. In past, I met several evangelist and one thing which I noticed is they all like talking to an extent where you really want to run away from them. I am not saying it is bad thing, but I am not convinced this is necessary. Why companies like Apple or Google don't have tech evangelist, or do they have?