I think nobody would like to think/know that it is the first one buying a product (Apple does not apply, hehe) or hiring the services of a company, I mean, not having proof that somebody has done it before, can mean that the product/service is not going to work properly, and in my opinion, is always much better to know for sure, that we are going to spend our money in something good enough.
Well, testimonies are a very powerful resource to establish a bond of trust with new customers; and in marketing they are a perfect tool to persuade people to decide to "buy" our product or service.
In a job I had when I was just a teenager, they told me once: "a satisfied customer means tens satisfied, an unsatisfied customer mens thousands unsatisfied." This would apply to the reviews, applying the same algorithm, if hundred potential customers see that we have positive reviews, maybe ten of them end up buying (1/10), but in the other hand, if we have mostly negative reviews, of every thousand potential clients, maybe only one end up buying (1/1000). What do you prefer?
For that reason, I consider very important that all those who have a website where they offer their product or services, invest some resources (mainly time) in a section with testimonials from customers giving their opinion (always specific, legitimate and real) about their experience with our product/service or at least, put a link to any tool where this kind of interaction exists with our users/clients (kind o a community), some examples that you must know: Google Business, Linkedin profile, Facebook page, Tripadvisor ...