How Necessary are Book Trailers?

I don't know about the rest of you, but I am really not a big fan of book trailers. I just feel like they're not really necessary, and some of them are just so poorly made (which is fair enough because it's book publishers making them rather than big budget Hollywood producers).

Here are some examples of kind of bad book trailers:

Reboot by Amy Tintera

OH MY GOD THE ACTING IS SO CRINGEWORTHY. And the weird CGI of the eyes argh I just can't take it.

Shatter Me by Tahereh Mafi

Seriously, they just really overuse the "shattering" animation. It was maybe okay the first two times, and then it was like OH GOD PLEASE STOP.

One of the only book trailers I've actually enjoyed is the one for Vicious by V.E. Schwab. I think it's because there wasn't actually any acting or anything in it. And it's really well made- the phrases it uses, the background music...everything in it makes you want to read the book. THIS is the sort of book trailer that should be done. Not some random crappy teenage actors.
Take a look at it below.

Are you a fan of book trailers? Link me to some good ones if you are so I can maybe change my mind about them.