Understanding how a processor works and what will happen if it is configured in a particular way is key to being able to write software or firmware that will function properly on the processor.
Usually the specifications for processor architecture is defined in (often extremely large) books in pdf format. For example the ARM Architecture Reference Manual contains thousands of pages and you need to be very keen to learn everything you need to know about a particular processor from this and to make use of that information. Keeping up with changes, fixes and new additions can be a full-time job!
ARM has now released version 8.2 of the ARM v8-A processor specification in machine readable form, with the intention of making implementation much easier for engineers.
For more details of why this is a good thing, Alastair Reid, one of ARM’s Senior Principal Research Engineers, has written a blog detailing some of the things you can do by downloading the XML files.