Listening to a language at slow speed: helpful or counterproductive?

So I’ve recently been trying to improve my listening skills since my reading skills are rather superior to my listening capabilities. Words that I know will fly right by me when spoken at native speed because I just don’t have the experience yet to recognize the words and phrases at high velocity.

However, I am able to recognize slower speech (children’s cartoons, documentaries, podcasts that are slow, etc) much more easily. But now I’m starting to wonder… is getting used to this slower speech actually helping more or is it a hindrance?

Recognizing every native speaker’s words and phrases at high velocity is impossible because each one has different way to express. Sometimes, I don’t understand Japanese, my native language, can not grab every word and phrase when some one speaks very rapidly. Just catching up key words is enough to follow this kind of talk. In my view, getting used to slower speeches is effective because we follow them almost completely ( I think) and memorize each word and phrase quite easily.

On one of my favorite sites they speak both at slow speed and at normal speed.

I also believe that listening to a foreign language at slow speed could be useful for levels from Elementary to Intermediate. But even more useful it would be if you listen the same text firstly at the slow speed and then at the normal speed to get accustomed to a new language.

Slow speed is good to learn new vocabulary but I think listening many times slow speed will not help understand normal speed.

To understand normal speed you need to listen normal speed again and again.