I saw a bad answer in the queue, voted it down and got -1 rep. Is this the expected behaviour of this site? If yes, what is the point of reviewing?
Yes, it is.
Downvoting an answer costs you -1 rep, regardless of whether you got there via a review queue or by any other means. It helps to encourage reviewers to "spend" their downvotes wisely.
If that bothers you, you can avoid downvoting — you can still leave comments explaining what is wrong, etc.
Note also that if the answer is ultimately deleted, you get the rep points back anyway.
@OlegMazurov the intent is "Sacrifice your rep for the good of the community". If the question or answer isn't bad enough that you are willing to lose a rep point over it, then it's not bad enough to downvote. If you are only in it for the rep, you arn't really participating in a community sense. From https://electronics.stackexchange.com/help/privileges/vote-down:
When should I vote down? Use your downvotes whenever you encounter an egregiously sloppy, no-effort-expended post, or an answer that is clearly and perhaps dangerously incorrect. You have a limited number of votes per day, and answer down-votes cost you a tiny bit of reputation on top of that; use them wisely.
What happens when I vote down? When you vote down, you are nudging that content "down" the page, so it will be seen by fewer people. Voting down answers is not something we want you to take lightly, so it is not free.
What are the alternatives to down-voting? The up-vote privilege comes first because that's what you should focus on: pushing great content to the top. Down-voting should be reserved for extreme cases. It's not meant as a substitute for communication and editing.
Think of it as the cost of doing business. A necessary expense to get the point across (pun intended).
That said, there are trade offs for that lost rep. Reviewing can lead to Badges which look nicer.