Quote Originally Posted by ironfist View Post
To be sure I understand:

Right:
Мой знакомый имеет большой дом
У моего знакомого большой дом

Wrong:
мой знакомый есть большой дом
It is because есть is an affirmative state of being (=is), and doesn't inherently indicate possession. The wrong sentence you listed literally means "my friend is big house".

The preposition у is used to mark the possessor. Recall that есть (=is) and нет (=is no[t]) in this context are opposites; there can only be one.

If у A(gen.) есть B, you can sometimes omit есть to reduce emphasis on the possession itself. But if у A(gen.) нет B(gen.), нет cannot be omitted.

У моего знакомого большой дом = (Lit.) At/by my friend (—) big house.