A service area can be useful for SEO to help Google understand where your service based company/website is relevant. If you don't have an address, it is also the only local SEO option available.
The article you posted is a good guide.
Do not try to use this as a way for your local business with an actual address to gain a broader reach. Use this strictly if you do not have an address.
It's harder to rank on the map without an address, but it is very common to see businesses that do. You must get a lot of reviews, create a lot of locally relevant content, and get backlinks from local publications, newspapers, etc.
Apple Maps does not support service areas.