A review request email can go out to customers a week or two after their item has shipped and nudge them to post a review on the site.
Unfortunately, reviews tend to skew negative. When people are happy with a product - even when they're very happy - they many times don't think to go and post a positive review, unless they're already in the habit of doing so.
It's typically when they're impassioned with anger or hatred for a product that they go searching that review form out!
So this is a great opportunity to remind customers to post a quick review about their experience. You can remind them that whether they have a negative or positive review to post, you're happy to have it.
Negative reviews even increase conversion rates, surprisingly enough!
When reviews are posted, they will show up in the Magento backend under Catalog > Reviews and Ratings > Customer Reviews > Pending Reviews: