Internal linking: does it really help and can it hurt?

Hello colleagues, I wanted to discuss the topic of internal linking. I have no dought that it's important to have a good internal linking structure in the header. I think that the user should have access to all important pages (categories, service pages, home page, etc) from any position. But I'm not sure if the internal linking really helps when you put to many links in the body of the text.
Yesterday I was auditing some of the commercial pages of the new client. And I was surprised to see soo many internal links (for a 600 word text) there were 7-10 internal links that point to other service pages, about us page, contact us page. I don't think that this is really useful, but correct me if I'm wrong or you think you have seen some improvements in your cases.

I must mention also that I had some nice results in reaching the TOP positions for the blog posts. When the internal linking was made between articles. I see here some profit to do it, because usually the articles/post aren't reachable from any position. So they don't get that much link juice as the pages from the header. Also need to note that I didn't use more than 3 internal links in the text.

So, here are some of my questions:

1. If you put to many links in the text, can it hurt the page, because you are sharing too much link juice?
2. Is there profit to link to pages that are set in the header?

Would be glad to hear your thoughts about this topic :)