Some Muslims who are either ignorant or of weak faith still commit many acts which Allah never allowed. Ignorance is not an excuse for doing something wrong or illegal, hence it is important to make an effort to learn what these muharramt or forbidden acts are, in order to avoid ever committing them.
The author, Shaykh Muhammad Slih al-Munajjid, explains many of the forbidden acts that have to do with calling on human beings and things other than Allah, worshipping the dead and circumambulating their graves, invoking prophets and the dead, magic, fortune-telling, believing in the power of astrologists and planets and other acts that go against the Islamic creed of monotheism (tawheed).
As such, this book of prohibitions regarding beliefs and acts of worship is a helpful resource for Muslims, if they are really practicing Islam and want to avoid committing great sins.