I used to do that, but now listen at 1x as it gives me time to have creative thoughts over what was said which helps me to retain the meaning behind the words.

I listen to most things above 1x speed specifically so that I don't have time to have creative thoughts about what I'm listening to, as that quickly leads to me no longer actually listening. Instead I have to specifically pause it if I want to stop and think about it.

Same here.

I often start with 1.5x and go up to 2x or 3x after a few minutes.

It's extremely important for online courses that would normally take weeks to watch and it starts feeling normal so quickly. When I go back to 1x it feels like people talk in slow-motion.

But I think quizzes are important in that context, otherwise the new knowledge won't solidify.

I'm always impressed of how much of my duolingo Spanish skills are still present, even if I didn't use the app for half a year or read any Spanish in that time.

Suppose it depends on what you're listening to and why, but I mostly listen to podcasts for entertainment, and I don't want to rush entertainment. I have enough trouble finding good stuff as it is.

I suspect this has a higher mental cost, leading to physical fatigue and slowed cognition later. We know chess players burn huge amounts of calories from thinking. IOW, there's no free lunch.

I find this also works great with instructional videos like pluralsight and lynda. It's easier on your working memory and concentration and if you relisten to tricky bits as you are going through you have a much deeper understanding that is more richly connected to your knowledge tree than plodding through at normal speed.

Audiobooks are purposefully read a slower than normal pace so non-native english speakers can follow along.

So, if you are a native speaker or you are fluent in the language, listening at a higher pace shouldn't be an issue.