With the roll-out of BERT and the previous algorithms by Google, they made a clear indication that rather than index keywords, they were moving towards indexing entities, in short, entity optimization - as entities are language agnostic, and hold universal significance. Schemas are essential for a website's SEO as they play an important role in entity recognition, as they give search engine bots a clear context of the website content, thereby enabling the content to be indexed as a rich result on SERPs.
In addition, with quality content a key factor for websites to rank on search, Google rolled out the E-A-T (Expertise, Authoritativeness, and Trustworthiness) framework for SEO and it has since become the guidelines for experts around the world to ensure their pages rank on search and schemas play a vital role in showing that the website meets E-A-T and the Quality Rater's Guidelines. In the words of Google, schema mark-up offers clues of the relationship of entities of the website and as it helps search engine bots understand the context of the content. In short, schemas help Google's EAT scoring process easier as they help the search engine reduce ambiguities between entities, create connections between them and provide additional information about an entity that Google might not have picked up when indexing a page.
Establishing that schemas do give search engines clear context of the website content which help them retrieve the content as a relevant answer for a query online, and that it helps a website meet E-A-T and the Quality Rater's Guidelines, schemas have in fact proved to boost the revenue of a business. How? You have to now consider Google as your homepage of your business, irrespective of whether you have a dedicated website or just a GMB profile. By giving the search engine surety of your website content - it's entities and relationships - you're allowing the search engine to display your content as rich results on SERPs.
This in turn paves way for higher clicks, impressions and click-through rate as the relevant information displayed on SERPs and its attractive nature prompts users to take an action. Thereby, not only improving your visibility online but increasing the chances of a conversion and your business's revenue.