Not just higher profits, but if you are self-published or have no reviews yet then your book is usually on the 400th page on anyone's search.
I have still told nobody I know about my book, it's kind of an experiment, because it would be easy for me to email blast everyone I know to like it, but I really want people to read it without pre-conception and so far no sales, even though it is free! (or 0.99 cents on Amazon as that's Amazon)
Not telling anyone you know is probably smart. _If_ you write outside of the genre your friends group usually reads and a bunch of them visit and buy your book out of curiosity on Amazon, it can negatively impact the categorization of your books.
"oh these people who usually read historical fiction are buying this new medical thriller. We will show this medical thriller to other people with the same buying habits!"
Only readers of historical fiction who aren't your friends probably won't bother picking up a medical thriller.
Regarding reviews, this is why many authors build ARC teams. Reviews are really important, so they send out advance review copies.
I have still told nobody I know about my book, it's kind of an experiment, because it would be easy for me to email blast everyone I know to like it, but I really want people to read it without pre-conception and so far no sales, even though it is free! (or 0.99 cents on Amazon as that's Amazon)