Using testimonials on your site (the right way) is always beneficial, whether your goal is more sales, or more subscribers, etc. Providing social proof that your product or blog is awesome will help convince people that giving your their money or time is worth their while. While you can certainly use written testimonials, video testimonials …Read: "Ask Yoast: How to use video testimonials?"
As the owner of an online store, you’d like people to find your shop. The right schema.org markup might help, as well as writing amazing content and preventing duplicate content on your site. Moreover, don’t forget to include some testimonials in the right spots!
This is of course closely related to user experience, usability and conversion.