It was a neat feature
It was a neat feature, and one, along with PDF export, that showed that you didn't need expensive closed-source software to get results.
Admittedly, I think I actually only used it once, to convert a presentation for display on the web (since, at that time, almost everyone had the Flash plug-in, which was more than you could say for either Impress itself or a certain other presentation application that you would have to pay for, with limited platform availability), but I was glad it was there.
But, yes, Flash is now a liability, and it would be great if there was an HTML 5 exporter instead.