Having a volunteer in the room to help with AV, room set up, other issues is awesome. Most conferences have this, so it stands out when this doesn’t happen.
Forcing speakers to use the conference laptop. Always a disaster. I will in fact refuse to speak at places that make me do this.
It can have a negative impact on my talk when A/V people are being really aggressive about setting up my laptop, I usually know more than they do about how to adjust settings.
The conference organizers did not tell me upfront that I am not able to use my laptop on stage and my material needs to be passed to the A/V crew. As it turned out the AV crew expected a ppt presentation file which I could not provide since I use a html5 presentation kit. “Fixing” these kinds of issues right before hitting the stage sucks.
One conference had a projector with a bad bulb that made all my dark blue slides with white text look like yellow with white text, so I was called out in the speaker feedback for making slides that were “unreadable.”
I was at a conference where I was both required to upload my slides to the conference site well in advance and then give it to the AV person after my talk. It cut into the time I could answer questions from the audience.
At the first conference I talked at I wasn’t really welcomed. I just went to the room where I talked (which was very small, they could have told me) and set up my own laptop and didn’t know if I was doing the right thing. The talk went terrible because it made me even more nervous.
Organisers who don’t know what resolution their projector is in advance and don’t have enough video dongles have ruined my day a few times.
I’ve had a few conferences where inadequate A/V facilities were present - stuff where the room was small, so they chose to eliminate the microphone, or the projector was on a normal-sized wall, and essentially un-viewable from mid-way through the room and back.