A couple of years ago I was invited to give a presentation at a job fair. The sponsors of the fair were allowed to make presentations about their companies. Everyone’s presentation tool of choice was PowerPoint.
One of the presenters, a senior technical writer, presented slides with too much information on each slide. If that wasn’t bad enough, some fonts were so small, they couldn’t be seen by the audience. She might as well have presented without the slides.
If this were an exception, I’d let it slide (unintended pun) but in my experience most people who are presenting don’t check how their slides appear when they are projected on a screen. If you use a projector, then sometimes fonts are distorted, sometimes colours can change, so it’s best to check in advance.
It can save you and your audience a lot of heartache.