When I started trying to post new videos, I had the same question. I asked my sister, who has been making videos on her YouTube channel for s couple years. Her opinion was that I should either just make like an overlay/watermark kind of thing, or just make a really short intro. I also started looking around at some of my favorite YouTubers to see what they were doing. I was surprised to see that most of them just went straight into their videos with no intro. The ones that did have intros had really short ones that were engaging.
I decided to go with just a short 4 second intro. I think someone previously mentioned something about branding. That's the thought process I had when I decided to do it. I figured I wanted something that would make my channel stand out from the others in my niche.
Anyhow, I'm no YouTube expert, but that's my thought. I love to read other's thoughts also.