As long as they are truthful they only report on the quality of the product and prevent many people of spending a lot of money from losing it by buying something that doesn't work.
Well, yeah sure. The problem is whether or not that's actually what's happening in any given circumstance. Most reviewers I've seen are more than happy to include personal opinion, and some will exagerrate points for the sake of getting views.
Things get even more fraught when the reviewer is a bigger company than the company whose product is being reviewed. For example the debacle with Linus Tech Tips and Billet labs that they were dragged for. That's the kind of coverage that absolutely can sink a company that seemingly only ever did exactly what they said they would.
Reviews are good if they present the important facts and generally act with integrity, but sometimes that's a really big 'if'.