From my experience making engineering videos, only teach topics you really know well (or are willing to learn very well). While preparing videos, you wouldn't believe the amount of times I've went "Hmmph, i don't really know why that works". Also, there's no room for mistakes/misinformation so you have to triple check your work before you publish it.
Or in my case, cross your fingers and hope you didn't say anything too stupid.
If I had to triple check everything I said/did in my videos, I'd never be able to produce any.
And yes, once a video is uploaded to youtube, you can't correct it without uploading a new one losing all your comments and views.