Schema markup helps search engine crawlers understand the components of web page content better, offering richer results to end-users. With proper markup, the likelihood of search results displaying rich snippets goes up.
For example, How To schema explains to search engines that the content includes step-by-step answers to a ‘How-To' question. The search engine is able to render the steps in the form of a rich result.
An immediate benefit of schema is increased CTR or click through rate. It is estimated that schemas drive 30% extra click throughs as users find richer and useful search results. Additionally, as search engines map content to more relevant searches, searchers end up clicking the results more, thus increasing organic traffic (and higher quality traffic) as well as search impressions.
Of Milestone's 9400+ schema projects executed, we have observed 25-60% increases in search impressions and organic traffic post implementations.