Here's the benefits:
Script coverage is actually a service that studios do. Screenwriters never see it. Studios have readers, and the readers give a screenplay a grade; Consider, Recommend, Pass, as well as a logline, synopsis, and reader's comments. Producers don't sit down and read stacks of scripts, they read the script coverage. Independent companies offer coverage and that's exactly what you'll get. This is a benefit if you want to see if your script is studio ready. The companies that do coverage use the same guidelines as the studios.
Script Evaluation (Analysis)
This is much different. This is a complete breakdown of the screenplay with comprehensive notes on improvement. It usually also includes script coverage. This is much more money.