1. Citing a given article by DOI, you need not to provide any auxiliary information about cited work - it is enough for full identification.
2. Having the DOI of an article one can easily check all metadata regarding authorship, keywords, including its journal or book, publisher and many others.
In one word the importance of using DOI in the publishing world is comparable to the importance of using EAN (usually expressed as barcodes) in the market of sale of goods.
Not only the DOI is important because it is useful for identification, but also if the RG score is important to you. Indeed, I noticed (after checking several scores and the offical criteria) that one "unofficial" factor to increase your score is the presence of a DOI number. Of course, that's only if you care about the RG score, which can be "nonsensical" as some users have put it.