Not placing backlinks inside text disadvantages

Hello, I have currently come across several schemes where people were able to drop backlinks for their websites from websites that have been compromised and they emphasised the point that they were leaving it within the text a lot. I do not endorse hacking nor plan on investing in these schemes but still would like to know why the "in-text" part was emphasised this much. Does it hurt to place your backlink as, say div display none somewhere else on the webpage? Because spying on my competitors I came to realise they had very few "in-content" backlinks and may div display none's.