There is a magic number for how many filler words are fine. It’s six. There are some people on the logical extreme, and they’ll say you need to hit zero. And sometimes that would be nice, to hit zero filler words, but in my opinion, don’t worry about it too much. Less than six per minute, and you’re probably fine. More than six per minute, and it’s probably a problem.
The reason it’s a problem is that your listeners’ brains have to process that uhh just like they do any other word. When you say the word door, or light, or jacket, for example, they have to momentarily think, what’s a door, or what’s a light, or what’s a jacket.
And when you say uhh, they have to process it too. Their brains go “what’s an uhh?” And then they realize, oh, it’s not a real word, I can discard it. And then they have to think, what was the word that came before it, and what’s the word that came after it, and they have to reconnect them.
So you’re up there talking, and you’re thinking, this is great, all these filler words give me time to think! But you are making your listeners do a lot of work, and because you’re so hard to listen to, your audience starts thinking, I don’t like this person, get this person off the stage.
Fortunately, the solution is pretty simple. You don’t have to stop taking time to think. Just fill the spaces with silence, not filler words.