Constructive or informative reviews are always a good tool to show other potential readers of what to expect from a novel. I would even say that just a simple review score alone in general can be a decent indicator of what to expect. But for them to be effective, they have to be allowed to exist regardless of the score, outside of the authors reach. If an author is allowed full rights to delete any kind of review at their own discretion, without oversight, the review system and score will lose all truthfulness and relevance.
I wouldn't have even considered writing this, if it wasn't because there is concrete evidence of this happening here. An author of a novel here on WN with a score of 4.8 has deleted my review with a 2.0 score 3 times in the last 2 days. Picture below shows how it looks in my System notifications. I went through 10 pages of reviews, sorted by newest, and found not a single review with a score below 4.0. I'm not sure anyone will believe that to be possible in any scenario, other than it being evidence that author deletes negative reviews to keep his average score high. And this is regardless of the reviews being constructive or informative or not. He deletes everything. I'd be happy to copy/paste my reviews that gets deleted if you guys want, but I don't want to turn this into a witchhunt against the author. He's not the problem, the site allowing authors to delete at their own discretion is.
All of this has been said before by other users on this site, but I feel it should be spoken of every once in a while to let others know what's happening.
To reiterate; review scores on this site are unrepresentative and untruthful to the novels, because authors can delete any review they want to keep their scores high.